SEC Form PRE 14A filed by Sensei Biotherapeutics Inc.

PRELIMINARY PROXY STATEMENT DATED APRIL 16, 2026—SUBJECT TO COMPLETION

Dear Sensei Stockholders:

You are cordially invited to attend the annual meeting of stockholders of Sensei Biotherapeutics, Inc. (“Sensei,” the “Company,” “we,” “our” or “us”), which will be held on Wednesday, June 10, 2026 at 11:00 a.m. Eastern Daylight Time (the “Annual Meeting”), unless postponed or adjourned to a later date. To facilitate stockholder participation in the Annual Meeting, the Annual Meeting will be held through a live webcast at www.proxydocs.com/SNSE. You will not be able to attend the meeting in person. The record date for the Annual Meeting is April 13, 2026. Only stockholders of record at the close of business on that date are entitled to notice of and to vote at the Annual Meeting or any adjournment thereof.

On February 17, 2026, the Company acquired Faeth Holdings Therapeutics, Inc., a Delaware corporation (“Faeth HoldCo”) and Faeth Therapeutics, LLC, a Delaware limited liability company and wholly owned subsidiary of Faeth HoldCo (“Faeth Subsidiary” and, together with Faeth HoldCo, “Faeth” or “Faeth Therapeutics”), in accordance with the terms of the Agreement and Plan of Merger, dated February 17, 2026 (the “Merger Agreement”), by and among the Company, Sapphire First Merger Sub, Inc., a Delaware corporation and a wholly owned subsidiary of the Company (“First Merger Sub”), Sapphire Second Merger Sub, LLC, a Delaware limited liability company and wholly owned subsidiary of the Company (“Second Merger Sub”), Faeth HoldCo and Faeth Subsidiary. Pursuant to the Merger Agreement, First Merger Sub merged with and into Faeth HoldCo, pursuant to which Faeth HoldCo was the surviving corporation and became a wholly owned subsidiary of the Company (the “First Merger”). Immediately following the First Merger, Faeth HoldCo merged with and into Second Merger Sub, pursuant to which Second Merger Sub was the surviving entity (together with the First Merger, the “Acquisition”).

Under the terms of the Merger Agreement, following the closing of the Acquisition (the “Closing”), (i) the Company issued to the stockholders of Faeth HoldCo an aggregate of 10,497.0980 shares of Series B Non-Voting Convertible Preferred Stock, par value $0.0001 per share (the “Series B Preferred Stock”) (as described below), each share of which is convertible into 1,000 shares of common stock of the Company, par value $0.0001 per share (“common stock”) (representing 10,497,098 shares on an as-converted-to-common basis and without giving effect to any beneficial ownership limitations), subject to certain conditions described below, (ii) an outstanding warrant to purchase shares of Faeth Subsidiary capital stock was converted into a warrant to purchase an aggregate of 2.1020 shares of Series B Preferred Stock (representing a warrant to purchase 2,102 shares of common stock on an as-converted-to-common basis and without giving effect to any beneficial ownership limitations) and (iii) all outstanding options to purchase Faeth Subsidiary common stock were assumed by the Company and converted into options to purchase an aggregate of 252,210 shares of common stock.

In connection with the Acquisition, on February 17, 2026, the Company entered into a Securities Purchase Agreement (the “Purchase Agreement”) with the purchasers named therein (the “Investors”), pursuant to which, on February 20, 2026 (the “PIPE Closing”), the Company issued and sold an aggregate of 14,440.395 shares of Series B Preferred Stock (the “PIPE Securities”) for an aggregate cash purchase price of approximately $200 million (such transaction, the “2026 Private Placement” and, together with the Acquisition and the other transactions and actions contemplated by the Merger Agreement, the “Acquisition Transactions”).

Subject to the receipt of stockholder approval of Proposals No. 3 and No. 4 (the “Required Company Stockholder Matters”), each outstanding share of Series B Preferred Stock will automatically convert into 1,000 shares of

common stock, subject to certain beneficial ownership limitations established by each holder. As a result of the transactions, immediately following the PIPE Closing, equityholders of the Company immediately prior to the acquisition owned approximately 4.9% of the common stock, equityholders of Faeth Therapeutics immediately prior to the acquisition owned approximately 40.6% of the common stock and the Investors in the 2026 Private Placement owned approximately 54.5% of the common stock, in each case, calculated on a fully-diluted, as-converted-to-common basis (and without giving effect to any beneficial ownership limitations) using the treasury stock method and based on the implied equity values of the Company and Faeth Therapeutics.

At the Annual Meeting, we will ask our stockholders:

As described in the accompanying proxy statement, in connection with the execution of the Merger Agreement, the Company and Faeth Subsidiary entered into stockholder support agreements (the “Support Agreements”) with certain of the Company’s officers and directors (solely in their capacity as stockholders), representing approximately 1.5% of shares of common stock outstanding on the record date. The Support Agreements provide that, among other things, each of the parties thereto has agreed to vote or cause to be voted all of the shares of common stock owned by such stockholder in favor of Proposals Nos. 3, 4, 5 and 6 at the Annual Meeting, subject to and in accordance with the terms of the Support Agreements.

After careful consideration, the Board has unanimously determined to recommend that our stockholders vote “FOR” each nominee named in the Director Election Proposal, “FOR” the Auditor Ratification Proposal, “FOR” the Conversion Proposal, “FOR” the Authorized Share Proposal, “FOR” the 2026 Plan Proposal, “FOR” the 2026 ESPP Proposal and “FOR” the Adjournment Proposal.

Shares of our common stock are currently listed on The Nasdaq Capital Market under the symbol “SNSE.” If the Required Company Stockholder Matters are approved and our Nasdaq Listing Application is approved, it is expected that we will change our name to “Faeth Therapeutics, Inc.” and our common stock will trade on The Nasdaq Capital Market under the symbol “FTH.”

More information about the Acquisition and the Required Company Stockholder Matters is contained in the accompanying proxy statement. We urge you to read the proxy statement carefully and in its entirety.

Your vote is important. Whether or not you expect to attend the Annual Meeting, please submit voting instructions for your shares promptly by using the directions on your Notice, or, if you elected to receive printed proxy materials by mail, on your proxy card, to vote by one of the following methods: (1) over the Internet before the Annual Meeting at www.proxypush.com/SNSE and during the Annual Meeting at www.proxydocs.com/SNSE, (2) by telephone by calling the toll-free number (866) 284-5317, or (3) if you elected to receive printed proxy materials by mail, by marking, dating, and signing your proxy card and returning it in the accompanying postage-paid envelope. Even if you have voted by proxy, you may still vote online if you attend the virtual Annual Meeting. Please note, however, that if your shares are held of record by a broker, bank, or other nominee and you wish to vote online at the Annual Meeting, you must obtain a proxy issued in your name from that record holder.

We thank you for your consideration and continued support.

This proxy statement is dated April , 2026 and is first being mailed to stockholders on or about April , 2026.

PRELIMINARY PROXY STATEMENT DATED APRIL 16, 2026—SUBJECT TO COMPLETION

SENSEI BIOTHERAPEUTICS, INC.

1405 Research Boulevard, Suite 125

Rockville, Maryland 20850

NOTICE OF ANNUAL MEETING OF STOCKHOLDERS

To Be Held On June 10, 2026

Dear Stockholder:

The Annual Meeting of stockholders of Sensei Biotherapeutics, Inc. (the “Company”) will be held on Wednesday, June 10, 2026 at 11:00 a.m. Eastern Daylight Time (the “Annual Meeting”). To facilitate stockholder participation in the Annual Meeting, the Annual Meeting will be held through a live webcast at www.proxydocs.com/SNSE. You will not be able to attend the meeting in person. The meeting will be held for the following purposes:

These items of business are more fully described in the Proxy Statement accompanying this Notice. This year’s Annual Meeting will be held virtually through a live webcast. You will be able to attend the Annual Meeting, submit questions and vote during the live webcast by visiting www.proxydocs.com/SNSE and entering the Control Number included in your proxy card, voting instruction form, or in the instructions that you received via email. Please refer to the additional logistical details and recommendations in the accompanying proxy statement. You may log-in beginning at 10:45 a.m. Eastern Daylight Time, on Wednesday, June 10, 2026. The record date for the Annual Meeting is April 13, 2026. Only stockholders of record at the close of business on that date are entitled to notice of and to vote at the meeting or any adjournment thereof.

By Order of the Board of Directors,

Christopher W. Gerry

President, General Counsel and Secretary

Rockville, Maryland

April , 2026

Table of Contents

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SENSEI BIOTHERAPEUTICS, INC.

1405 Research Boulevard, Suite 125

Rockville, Maryland 20850

PROXY STATEMENT

For The 2026 Annual Meeting of Stockholders

To Be Held on June 10, 2026

QUESTIONS AND ANSWERS ABOUT THESE PROXY MATERIALS AND VOTING

Why did I receive a notice regarding the availability of proxy materials on the internet?

Pursuant to rules adopted by the SEC, we have elected to provide access to our proxy materials over the internet. Accordingly, we have sent you a Notice of Internet Availability of Proxy Materials (the “Notice”) because the Board of Directors (the “Board” or “Board of Directors”) of Sensei Biotherapeutics, Inc. (the “Company”) is soliciting your proxy to vote at the 2026 Annual Meeting of Stockholders, including at any adjournments or postponements of the meeting. All stockholders will have the ability to access the proxy materials on the website referred to in the Notice or request to receive a printed set of the proxy materials. Instructions on how to access the proxy materials over the internet or to request a printed copy may be found in the Notice.

We intend to mail the Notice on or about April    , 2026 to all stockholders of record entitled to vote at the annual meeting.

How do I attend the Annual Meeting?

To facilitate stockholder participation in the Annual Meeting, this year the Annual Meeting will be held through a live webcast at www.proxydocs.com/SNSE. You will not be able to attend the Annual Meeting in person. If you attend the Annual Meeting online, you will be able to vote and submit questions at www.proxydocs.com/SNSE.

You are entitled to attend the Annual Meeting if you were a stockholder as of the close of business on April 13, 2026, the record date, or hold a valid proxy for the meeting. To be admitted to the Annual Meeting, you will need to visit www.proxydocs.com/SNSE and enter the Control Number found next to the label “Control Number” on your proxy card, or voting instruction form, or in the email sending you the Proxy Statement. If you are a beneficial stockholder, you should contact the bank, broker or other institution where you hold your account well in advance of the meeting if you have questions about obtaining your control number/ proxy to vote.

Whether or not you participate in the Annual Meeting, it is important that you vote your shares.

We encourage you to access the Annual Meeting before it begins. Online check-in will start approximately 15 minutes before the meeting on June 10, 2026.

What if I cannot find my Control Number?

We will have access to a list of control numbers for registered stockholders in the event of a lost number. You may also consult your Mediant Relationship Manager for assistance. Typically, “guest” access is not permitted. Please consult with your Mediant Relationship Manager if you would like to permit guest access.

If you are a beneficial owner (that is, you hold your shares in an account at a bank, broker or other holder of record), you will need to contact that bank, broker or other holder of record to obtain your Control Number prior to the Annual Meeting.

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Will a list of record stockholders as of the record date be available?

A list of our record stockholders as of the close of business on April 13, 2026 will be available for inspection at our corporate office for the 10 days ending on the day before the Annual Meeting. If you want to inspect the stockholder list, call our office at (240) 243-8000 to speak with our Investor Relations department to schedule an appointment.

Where can we get technical assistance?

We will have technicians ready to assist you with any technical difficulties you may have accessing the Annual Meeting. If you encounter any difficulties accessing the virtual-only Annual Meeting platform, including any difficulties voting or submitting questions, you may call the technical support number that will be posted in your instructional email. The technical support number will not be posted publicly; it will be provided to meeting attendees via e-mail one hour prior to the meeting start time.

For the Annual Meeting, how do we ask questions of management and the board?

Stockholders may submit questions that are relevant to our business in advance of the Annual Meeting. If you are a stockholder, you may submit a question in advance of the meeting at www.proxydocs.com/SNSE after logging in with your Control Number. We do not intend to post questions or answers to stockholder questions received during the Annual Meeting on our website.

Who can vote at the Annual Meeting?

Only stockholders of record at the close of business on April 13, 2026 will be entitled to vote at the Annual Meeting. On this record date, there were 1,341,140 shares of common stock outstanding and entitled to vote. On the record date, there were 24,937.493 shares of Series B Preferred Stock issued and outstanding; however, the Series B Preferred Stock are not entitled to vote on the matters being considered at the Annual Meeting. Because we did not issue any shares of our common stock in the Acquisition Transactions, none of our outstanding shares of common stock as of the record date are excluded from voting on the Conversion Proposal pursuant to Nasdaq Listing Rules.

Stockholder of Record: Shares Registered in Your Name

If on April 13, 2026 your shares were registered directly in your name with our transfer agent, Equiniti Trust Company, LLC (formerly American Stock Transfer & Trust Company, LLC), then you are a stockholder of record. As a stockholder of record, you may vote virtually at the meeting or vote by proxy. Whether or not you plan to attend the meeting, we urge you to fill out and return the proxy card or vote by proxy over the telephone or on the internet as instructed below to ensure your vote is counted.

Beneficial Owner: Shares Registered in the Name of a Broker or Bank

If on April 13, 2026 your shares were held, not in your name, but rather in an account at a brokerage firm, bank, dealer or other similar organization, then you are the beneficial owner of shares held in “street name” and the Notice is being forwarded to you by that organization. The organization holding your account is considered to be the stockholder of record for purposes of voting at the Annual Meeting. As a beneficial owner, you have the right to direct your broker or other agent regarding how to vote the shares in your account. You are also invited to attend the Annual Meeting. However, since you are not the stockholder of record, you may not vote your shares virtually at the meeting unless you request and obtain a valid legal proxy from your broker or other agent.

What am I voting on?

There are seven matters scheduled for a vote:

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With respect to the Conversion Proposal, stockholders should note that a “change of control” as described under Nasdaq Listing Rule 5635(b) applies only with respect to the application of such rule and does not constitute a “change of control” for purposes of Delaware law or our organizational documents.

What if another matter is properly brought before the meeting?

The Board of Directors knows of no other matters that will be presented for consideration at the Annual Meeting. If any other matters are properly brought before the meeting, it is the intention of the persons named in the accompanying proxy to vote on those matters in accordance with their best judgment.

Are stockholders being asked to vote on the Merger Agreement or the Acquisition described herein?

No. The Acquisition was completed on February 17, 2026 and we are not required to seek, nor are we seeking, stockholder approval of the Acquisition or the Merger Agreement. Rather, for purposes of complying with the Nasdaq Listing Rules, we are seeking stockholder approval for the issuance of shares of common stock of the Company upon conversion of the outstanding shares of Series B Preferred Stock that we issued in the Acquisition. The Company and Faeth discussed various potential transaction structures and, due to the desire of both parties to consummate the Acquisition at the earliest possible time, the Board approved a transaction structure that did not require the approval of the stockholders of the Company for the consummation of the Merger.

How do I vote?

You may either vote “For” all of the nominees to the Board of Directors or you may “Withhold” your vote for any nominee you specify. For the other matters to be voted on, you may vote “For” or “Against” or abstain from voting.

The procedures for voting are:

Stockholder of Record: Shares Registered in Your Name

If you are a stockholder of record, you may vote virtually at the Annual Meeting or vote by proxy in one of three ways: online, by telephone or using the proxy card that you may request or that we may elect to deliver at a later

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time. Whether or not you plan to attend the meeting, we urge you to vote by proxy to ensure your vote is counted. You may still attend the Annual Meeting and vote virtually even if you have already voted by proxy.

To vote during the Annual Meeting, if you are a stockholder of record as of the record date, follow the instructions provided via e-mail after registering at www.proxydocs.com/SNSE. You will need to enter the Control Number found on your Notice of Internet Availability or notice you receive or in the email sending you the proxy statement.

To vote prior to the Annual Meeting you may vote via the Internet at www.proxypush.com/SNSE; by telephone; or by completing and returning the proxy card or voting instruction form, as described below.

Beneficial Owner: Shares Registered in the Name of Broker or Bank

If you are a beneficial owner of shares registered in the name of your broker, bank or other agent, you should have received a notice containing voting instructions from that organization rather than from us. Please follow the voting instructions in the notice to ensure that your vote is counted. Alternatively, you may vote by telephone or over the internet as instructed by your broker or bank. You may access and vote at the meeting by registering to attend the meeting at www.proxydocs.com/SNSE using your control number on your voting instruction form and by requesting a valid proxy from your broker, bank or other agent.

How many votes do I have?

On each matter to be voted upon, you have one vote for each share of common stock you own as of April 13, 2026.

What happens if I do not vote?

Stockholder of Record: Shares Registered in Your Name

If you are a stockholder of record and do not vote by completing your proxy card, by telephone or through the internet at the Annual Meeting, your shares will not be voted.

Beneficial Owner: Shares Registered in the Name of Broker or Bank

If you are a beneficial owner and do not instruct your broker, bank, or other agent how to vote your shares, the question of whether your broker or nominee will still be able to vote your shares depends on whether the New York Stock Exchange (“NYSE”) deems the particular proposal to be a “routine” matter. Brokers and nominees can use their discretion to vote “uninstructed” shares with respect to matters that are considered to be “routine,”

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but not with respect to “non-routine” matters. Under the rules and interpretations of the NYSE, “non-routine” matters are matters that may substantially affect the rights or privileges of stockholders, such as mergers, stockholder proposals, elections of directors (even if not contested), executive compensation (including any advisory stockholder votes on executive compensation and on the frequency of stockholder votes on executive compensation), and certain corporate governance proposals, even if management-supported. Accordingly, your broker or nominee may not vote your shares on Proposal No. 1 (the Director Election Proposal), Proposal No. 3 (the Conversion Proposal), Proposal No. 4 (the Authorized Share Proposal), Proposal No. 5 (the 2026 Plan Proposal), Proposal No. 6 (the 2026 ESPP Proposal) or Proposal No. 7 (the Adjournment Proposal), but may vote your shares on Proposal No. 2 (the Auditor Ratification Proposal) even in the absence of your instruction.

What if I return a proxy card or otherwise vote but do not make specific choices?

If you return a signed and dated proxy card or otherwise vote without marking voting selections, your shares will be voted, as applicable, “FOR” each nominee named in the Director Election Proposal, “FOR” the Auditor Ratification Proposal, “FOR” the Conversion Proposal, “FOR” the Authorized Share Proposal, “FOR” the 2026 Plan Proposal, “FOR” the 2026 ESPP Proposal and “FOR” the Adjournment Proposal. If any other matter is properly presented at the meeting, your proxyholder (one of the individuals named on your proxy card) will vote your shares using his or her best judgment.

Who is paying for this proxy solicitation?

The Company will pay for the entire cost of soliciting proxies. In addition to our proxy materials, our directors and employees may also solicit proxies virtually, by telephone, or by other means of communication. Directors and employees will not be paid any additional compensation for soliciting proxies. We will also reimburse brokerage firms, banks and other agents for the cost of forwarding proxy materials to beneficial owners. In addition, we have retained Innisfree as a proxy solicitor to solicit proxies for the Annual Meeting and provide related advice and information support, for a service fee of $30,000 and the reimbursement of customary disbursements

What does it mean if I receive more than one Notice?

If you receive more than one Notice, your shares may be registered in more than one name or in different accounts. Please follow the voting instructions on the Notice to ensure that all of your shares are voted.

Can I change my vote after submitting my proxy?

Stockholder of Record: Shares Registered in Your Name

Yes. You can revoke your proxy at any time before the final vote at the meeting. If you are the record holder of your shares, you may revoke your proxy in any one of the following ways:

Your most current proxy card or telephone or internet proxy is the one that is counted.

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Beneficial Owner: Shares Registered in the Name of Broker or Bank

If your shares are held by your broker or bank as a nominee or agent, you should follow the instructions provided by your broker or bank.

When are stockholder proposals and director nominations due for next year’s Annual Meeting?

To be considered for inclusion in next year’s proxy materials, your proposal must be submitted in writing by December     , 2026 to our Corporate Secretary at 1405 Research Blvd, Suite 125, Rockville, Maryland 20850. If you wish to nominate an individual for election at, or bring business other than through a stockholder proposal before, the 2027 Annual Meeting, you must deliver your notice to our Corporate Secretary at the address above between February 10, 2027 and March 12, 2027. Your notice to the Corporate Secretary must set forth information specified in our bylaws, including your name and address and the class and number of shares of our stock that you beneficially own. In addition to satisfying the requirements under our bylaws, to comply with the universal proxy rules, stockholders who intend to solicit proxies in support of director nominees other than our nominees must provide notice that sets forth the information required by Rule 14a-19 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”).

If you propose to bring business before an Annual Meeting other than a director nomination, your notice must also include, as to each matter proposed, the following: (1) a brief description of the business desired to be brought before the Annual Meeting and the reasons for conducting that business at the Annual Meeting and (2) any material interest you have in that business. If you propose to nominate an individual for election as a director, your notice must also include, as to each person you propose to nominate for election as a director, the following: (1) the name, age, business address and residence address of the person, (2) the principal occupation or employment of the person, (3) the class and number of shares of our stock that are owned of record and beneficially owned by the person, (4) the date or dates on which the shares were acquired and the investment intent of the acquisition and (5) any other information concerning the person as would be required to be disclosed in a proxy statement soliciting proxies for the election of that person as a director in an election contest (even if an election contest is not involved), or that is otherwise required to be disclosed pursuant to Section 14 of the Exchange Act, and the rules and regulations promulgated under the Exchange Act, including the person’s written consent to being named as a nominee and to serving as a director if elected. We may require any proposed nominee to furnish other information as we may reasonably require to determine the eligibility of the proposed nominee to serve as an independent director or that could be material to a reasonable stockholder’s understanding of the independence, or lack of independence, of the proposed nominee.

For more information, and for more detailed requirements, please refer to our Amended and Restated Bylaws, filed as Exhibit 3.2 to our Annual Report on Form 10-K, filed with the Securities and Exchange Commission (the “SEC”) on March 30, 2026.

How are votes counted?

Votes will be counted by the inspector of election appointed for the meeting, who will separately count, for Proposal No. 1 (the Director Election Proposal), votes “For,” “Withhold” and broker non-votes, and with respect to the Proposal No. 2 (the Auditor Ratification Proposal), Proposal No. 3 (the Conversion Proposal), Proposal No. 4 (the Authorized Share Proposal), Proposal No. 5 (the 2026 Plan Proposal), Proposal No. 6 (the 2026 ESPP Proposal) and Proposal No. 7 (the Adjournment Proposal), votes “For,” “Against” and abstentions.

For Proposal No. 1, abstentions are not applicable and “Withhold” votes and broker non-votes will have no effect and will not be counted toward the vote total for any of the director nominees. For Proposal No. 2, this proposal is considered a “routine” matter under applicable NYSE rules. Accordingly, if you hold your shares in street name and do not provide voting instructions to your broker, bank or other agent that holds your shares, your broker, bank or other agent has discretionary authority to vote your shares on this proposal, and we do not expect there to be broker non-votes on this matter. Abstentions will be counted and will have the same effect as “Against” votes.

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For Proposals No. 3, No. 4, No. 5 and No. 6, only “For” and “Against” votes will be counted. Abstentions and broker non-votes will have no effect and will not be counted as votes cast for purposes of determining whether any such proposal has been approved.

For Proposal No. 7, abstentions will be counted and will have the same effect as “Against” votes. Broker non-votes, if any, will have no effect and will not be counted toward the vote total for this proposal.

What are “broker non-votes”?

As discussed above, when a beneficial owner of shares held in “street name” does not give instructions to the broker or nominee holding the shares as to how to vote on matters deemed by the NYSE to be “non-routine,” the broker or nominee cannot vote the shares. These unvoted shares are counted as “broker non-votes.”

How many votes are needed to approve each proposal?

The following table summarizes the minimum vote needed to approve each proposal and the effect of abstentions and broker non-votes.

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What is the quorum requirement?

A quorum of stockholders is necessary to hold a valid meeting. A quorum is present if stockholders holding at least a majority of the outstanding shares entitled to vote are present at the Annual Meeting virtually or represented by proxy. On the record date, there were 1,341,140 shares outstanding and entitled to vote. Thus, the holders of 670,571 shares must be present virtually or represented by proxy at the Annual Meeting to have a quorum.

Your shares will be counted towards the quorum only if you submit a valid proxy (or one is submitted on your behalf by your broker, bank or other nominee) or if you vote online at the meeting. Abstentions and broker non-votes will be counted towards the quorum requirement. If there is no quorum, either the chairman of the Annual Meeting or the holders of a majority of shares present at the Annual Meeting virtually or represented by proxy may adjourn the meeting to another date.

How can I find out the results of the voting at the Annual Meeting?

Preliminary voting results will be announced at the Annual Meeting. In addition, final voting results will be published in a current report on Form 8-K that we expect to file within four business days after the Annual Meeting.

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CAUTIONARY INFORMATION REGARDING FORWARD LOOKING STATEMENTS

All statements other than statements of historical fact included in this Proxy Statement including, without limitation, statements regarding our business strategy and the plans and objectives of management for future operations, are forward-looking statements. When used in this Proxy Statement, words and phrases such as “aim,” “anticipate,” “assume,” “believe,” “can,” “continue,” “could,” “designed to,” “estimate,” “evaluate,” “expect,” “explore,” “intend,” “intended to,” “likely,” “may,” “might,” “objective,” “ongoing,” “plan,” “potential,” “predict,” “project,” “pursue,” “seek,” “should,” “to be,” “will,” and “would,” or the negative of such terms or other similar expressions, as they relate to us or our management, identify forward-looking statements. Any statements in this Proxy Statement about our expectations, beliefs, plans, objectives, assumptions or future events or performance are not historical facts and are forward-looking statements within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act.

These forward-looking statements include statements regarding: our expectations for the Board, management team, Company name and ticker if the Nasdaq Listing Application and the Required Company Stockholder Matters are approved; our ability to meet Nasdaq’s initial listing standards; the potential benefits of the Authorized Share Proposal; and the Company’s ability to realize the anticipated benefits of the Acquisition, including with respect to the development of PIKTOR.

These statements involve known and unknown risks, uncertainties and other factors that may cause our actual results, levels of activity, performance or achievements to be materially different from the information expressed or implied by these forward-looking statements. Except as required by law, we assume no obligation to update these forward-looking statements publicly, or to revise any forward-looking statements to reflect events or developments occurring after the date of this Proxy Statement, even if new information becomes available in the future. You should refer to the Risk Factors section of this Proxy Statement and of our Annual Report for a discussion of important factors that may cause our actual results to differ materially from those expressed or implied by our forward-looking statements.

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DESCRIPTION OF THE TRANSACTIONS

Acquisition of Faeth Therapeutics

In the ordinary course of business, the Board regularly reviewed the strategy, prospects and financial condition of the Company, including opportunities and risks associated with the Company’s product candidates and strategic alternatives potentially available to the Company. Beginning in mid-2024, in light of challenging conditions in the biotechnology capital markets and the Company’s declining cash balance, the Board, together with the Company’s management, Sidley Austin LLP (“Sidley”), the Company’s legal counsel, and Lucid Capital Markets, LLC (“Lucid Capital Markets”), the Company’s financial advisor, began to evaluate strategic alternatives available to the Company, including a potential sale, business combination or liquidation, as well as licensing and other business development opportunities related to its lead product candidate, solnerstotug (formerly SNS-101). Over the course of the following year, the Board pursued a dual-track strategy of financing and business development outreach alongside exploration of potential reverse merger transactions. During this period, Lucid Capital Markets and the Company’s management team reviewed more than 25 potential reverse merger candidates, and the Company’s management and banking partners conducted extensive investor outreach in an effort to obtain financing. These efforts produced neither attractive reverse merger options nor viable financing or partnership options sufficient to fund solnerstotug through a Phase 2 clinical trial.

In October 2025, the Board authorized management to initiate a comprehensive review process and re-engaged Lucid Capital Markets in connection with that review, in light of, among other things, the Company’s cash position, the inability to secure adequate financing despite extensive efforts, and the challenges of raising additional capital in a volatile biotechnology market.

Following Lucid Capital Markets’ December 2025 outreach process and the Board’s review of strategic alternatives available to the Company, including acquisition, licensing, wind-down and reverse merger alternatives, the Company focused its efforts on Faeth Therapeutics as a potential business combination partner. The Board determined that Faeth Therapeutics merited serious consideration based on the development status of Faeth Therapeutics’ lead program, PIKTOR, an investigational all-oral, multi-node inhibitor of the PI3K/AKT/mTOR pathway in development for endometrial and breast cancer, the public financing momentum around Faeth Therapeutics during 2025, including Faeth Therapeutics’ $25 million strategic financing in October 2025, and the opportunity to pair a business combination with a substantial concurrent financing.

Beginning on January 9, 2026 and continuing through February 17, 2026, representatives of the Company’s management, Sidley, Lucid Capital Markets, Faeth Therapeutics’ management, Cooley LLP, Faeth Therapeutics’ legal counsel, and Leerink Partners, Faeth Therapeutics’ financial advisor, conducted business, financial, legal, tax, intellectual property and other due diligence with respect to the Company, Faeth Therapeutics and the potential transaction.

On February 17, 2026, the Company acquired Faeth Therapeutics pursuant to the Merger Agreement, pursuant to which First Merger Sub merged with and into Faeth HoldCo, pursuant to which Faeth HoldCo was the surviving corporation and became a wholly owned subsidiary of the Company. Immediately following the First Merger, Faeth HoldCo merged with and into Second Merger Sub, pursuant to which Second Merger Sub was the surviving entity. The simultaneous sign-and-close structure of the Acquisition, combined with the concurrent private placement financing (as described below), preserved cash that would otherwise have been spent during a more extended closing process and enabled the financing to close more quickly and with greater certainty.

The Acquisition was structured as a stock-for-stock transaction pursuant to which all of Faeth Subsidiary’s outstanding equity interests were exchanged based on a fixed exchange ratio for aggregate consideration of 10,497.0980 shares of Series B Preferred Stock, each share of which is convertible into 1,000 shares of common stock (representing 10,497,098 shares on an as-converted-to-common basis and without giving effect to any beneficial ownership limitations), subject to certain conditions described below under Proposal No. 3. In

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addition, an outstanding warrant to purchase shares of Faeth Subsidiary capital stock was converted into a warrant to purchase an aggregate of 2.1020 shares of Series B Preferred Stock (representing a warrant to purchase 2,102 shares of common stock on an as-converted-to-common basis and without giving effect to any beneficial ownership limitations) and all outstanding options to purchase Faeth Subsidiary common stock were assumed by the Company and converted into options to purchase an aggregate of 252,210 shares of common stock. The Series B Preferred Stock was a newly designated series of preferred stock and was intended to have economic rights equivalent to our common stock, but with no voting rights. The rights of the Series B Preferred Stock are set forth in the Certificate of Designation of Series B Non-Voting Convertible Preferred Stock (the “Certificate of Designation”) that we filed with the Secretary of State of the State of Delaware. Please see “Description of Series B Preferred Stock” under Proposal No. 3 for a complete description of the Certificate of Designation and the rights of the Series B Preferred Stock. The Acquisition Transactions were approved by the Board, as well as the board of directors and stockholders of Faeth Therapeutics.

In connection with the execution of the Merger Agreement, the Company and Faeth Subsidiary entered into Support Agreements with certain of our officers and directors (solely in their capacity as stockholders), representing approximately 1.5% of shares of common stock outstanding on the record date. The Support Agreements provide that, among other things, each of the parties thereto has agreed to vote or cause to be voted all of the shares of common stock beneficially owned by such stockholder in favor of Proposals Nos. 3, 4, 5 and 6 at the Annual Meeting, subject to and in accordance with the terms of the Support Agreements. The Acquisition has already been consummated, and stockholder approval of the Acquisition or the Merger Agreement is not being sought at this Annual Meeting.

2026 Private Placement

Concurrently with the Acquisition, we entered into the Purchase Agreement with the Investors with respect to the 2026 Private Placement, pursuant to which, on February 20, 2026, the Company issued and sold an aggregate of 14,440.395 shares of Series B Preferred Stock, each share of which is convertible into 1,000 shares of common stock (representing 14,440,395 shares on an as-converted-to-common basis and without giving effect to any beneficial ownership limitations), subject to certain conditions described below under Proposal No. 3, at a price of $13,850 per share of Series B Preferred Stock (or approximately $13.85 per share on an as-converted-to-common basis) for aggregate gross proceeds of approximately $200 million. On an as-converted-to-common basis (excluding shares underlying warrants and equity awards) and after accounting for the Acquisition Transactions, the total number of outstanding shares of common stock was 26,199,178 immediately following the PIPE Closing.

On February 17, 2026, we entered into a Registration Rights Agreement (the “RRA”) with the Investors. Pursuant to the RRA, we are obligated to prepare and file a resale registration statement with the SEC within 75 calendar days following the closing of the 2026 Private Placement. The RRA also contains customary terms, including an obligation to indemnify the Investors and certain affiliates from certain liabilities relating to any misstatements or omissions in the resale registration statement.

As a result of the transactions, immediately following the PIPE Closing, equityholders of the Company immediately prior to the acquisition owned approximately 4.9% of the common stock, equityholders of Faeth Therapeutics immediately prior to the acquisition owned approximately 40.6% of the common stock and the Investors in the 2026 Private Placement owned approximately 54.5% of the common stock, in each case, calculated on a fully-diluted, as-converted-to-common basis (and without giving effect to any beneficial ownership limitations) using the treasury stock method and based on the implied equity values of the Company and Faeth Therapeutics.

Under the terms of the Merger Agreement and the Purchase Agreement, we are required to call and hold a meeting of our stockholders, as promptly as practicable following the date of the Merger Agreement and pursuant to the Nasdaq Stock Market Rules, to obtain the requisite approval from our legacy stockholders for, among other things, Proposals Nos. 3, 4, 5 and 6.

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On February 18, 2026, the Company publicly announced the Acquisition Transactions and filed a Current Report on Form 8-K attaching the Merger Agreement and related transaction documents. In that announcement, the Company stated that, following the Acquisition, its lead program would be PIKTOR and that the Company expected to use the proceeds of the 2026 Private Placement financing primarily to advance PIKTOR through key clinical milestones, including topline data from an ongoing Phase 2 trial in second-line advanced endometrial cancer and the initiation of a Phase 1b trial in HR+/HER2- advanced breast cancer, and to complete the ongoing Phase 1/2 trial of solnerstotug.

The foregoing summary of the terms of the Merger Agreement, the Certificate of Designation, the Purchase Agreement and the RRA are not complete and are qualified in their entirety by the provisions of Merger Agreement, the Certificate of Designation, the form of Purchase Agreement and the form of RRA, which are filed as Exhibits 2.1, 3.1, 10.1 and 10.2, respectively, to our Current Report on Form 8-K, filed with the SEC on February 18, 2026.

Accounting Treatment

With respect to the Acquisition, we determined that we were the acquiror for accounting purposes under ASC 805-10-25-4 and ASC 805-10-55-11. The primary factors considered were (a) the relative voting rights in the combined entity not resulting in a change of control, (b) the pre-Acquisition members of the Board maintained control of the Board, and (c) the pre-Acquisition members of senior management remained the same at the closing of the Acquisition Transactions, other than the newly appointed Chief Operating Officer. Next, we considered whether the Acquisition should be defined as a business under ASC 805. ASC 805-10-55-5A through 55-5C describe a screen test to determine whether an acquired set of assets and activities is not a business. We determined that substantially all (greater than 90%) of the fair value of the assets acquired were concentrated in a single asset, PIKTOR, an investigational, proprietary, all-oral combination of serabelisib and sapanisertib that is designed to inhibit multiple nodes of the PI3K/AKT/mTOR pathway through PI3K-alpha and dual mTORC1/2 targeting. Accordingly, we treated the Acquisition as an asset acquisition for accounting purposes.

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RISK FACTORS

You should carefully consider the risks described below, together with all of the other information contained in this proxy statement (including the unaudited pro forma financial information included elsewhere in this proxy statement), in deciding how to vote on matters being considered at the Annual Meeting. In addition, for a discussion of risks relating to our business, financial condition, results of operations and industry generally, you should review the risk factors described under the caption “Risk Factors” in our Annual Report on Form 10-K for the fiscal year ended December 31, 2025, filed with SEC on March 30, 2026, as such risk factors may be updated from time to time in our subsequent reports filed with the SEC.

Pursuant to the terms of the Acquisition, we are required to recommend that our stockholders approve the conversion of all outstanding shares of our Series B Preferred Stock into shares of our common stock. We must also obtain stockholder approval of an amendment to our certificate of incorporation to increase the number of shares we are authorized to issue. We cannot guarantee that our stockholders will approve these matters, and if they fail to do so we may be required to settle such shares in cash and our operations may be materially harmed.

Under the terms of the Merger Agreement and the Purchase Agreement, as promptly as practicable following the date of the Merger Agreement and pursuant to the Nasdaq Stock Market Rules, we are required to call and hold a meeting of our stockholders to obtain the requisite approval from our legacy stockholders for, among other things, (i) the Conversion Proposal, (ii) the Authorized Share Proposal, (iii) the 2026 Plan Proposal and (iv) the 2026 ESPP Proposal. If we fail to receive sufficient proxies to constitute a quorum or to obtain the required vote on the Required Company Stockholder Matters and/or the Nasdaq Listing Application is not approved, we would be required to adjourn the Annual Meeting one or more times for up to 30 days per adjournment. If stockholder approval of the Required Company Stockholder Matters or approval of the Nasdaq Listing Application are still not obtained following such adjournment(s), we will be obligated to continue soliciting stockholder approval at subsequent annual or special meetings of our stockholders, held at intervals of no more than six months, until such approvals are obtained, which would be time consuming and costly.

There can be no assurance that our legacy stockholders will approve the Required Company Stockholder Matters. If our legacy stockholders do not approve the Authorized Share Proposal, we would be unable to issue the additional shares of our common stock necessary to complete the conversion of Series B Preferred Stock into our common stock, and may be unable to satisfy our other capital needs, which could have a material adverse effect on our business, financial condition, and prospects.

Additionally, if the Required Company Stockholder Matters are not approved by the date that is six months following the initial issuance date of the Series B Preferred Stock, the holders of the Series B Preferred Stock would be entitled to require us to settle their shares of our common stock underlying the Series B Preferred Stock for cash at a price per share equal to the fair value of our common stock at such time as described in the Certificate of Designation. If we are forced to cash settle a significant amount of the shares of our common stock underlying the Series B Preferred Stock, it could materially affect our results of operations, business and financial condition.

Failure to obtain approval of the Nasdaq Listing Application could materially affect our results of operations, business and financial condition.

Pursuant to the Merger Agreement, in order to permit the waiver of the beneficial ownership limitations applicable to the Series B Preferred Stock and take other actions following the consummation of the Acquisition, which would constitute a “change of control” under Nasdaq Listing Rule 5110(a), we are required to use our reasonable best efforts to file the Nasdaq Listing Application. The Nasdaq Listing Application must be conditionally approved prior to the date of our stockholder meeting to approve the Required Company Stockholder Matters. If we fail to meet the Nasdaq listing requirements and Nasdaq does not approve the Nasdaq

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Listing Application, we will be required to adjourn our stockholder meeting to approve the Required Company Stockholder Matters one or more times for up to 30 days per adjournment, continue to use our reasonable best efforts to obtain approval of the Nasdaq Listing Application and to continue soliciting stockholder approval of the Required Company Stockholder Matters at subsequent annual or special meetings of our stockholders, held at intervals of no more than six months, until such approval and the approval of the Required Company Stockholder Matters are obtained, which would be time consuming and costly. Additionally, if the Required Company Stockholder Matters are not approved by the date that is six months following the initial issuance date of the Series B Preferred Stock, the holders of the Series B Preferred Stock would be entitled to require us to settle their shares of Series B Preferred Stock for cash at a price per share equal to the fair value of the Series B Preferred Stock at such time as described in the Certificate of Designation. If we are forced to cash settle a significant amount of the shares of our common stock underlying the Series B Preferred Stock, it could materially affect our results of operations, business and financial condition. We cannot assure you that we will be able to meet Nasdaq’s initial listing standards. Furthermore, if we fail to obtain approval of the Nasdaq Listing Application, we may be unable to execute on our plans for the Company following the Acquisition, which could materially affect our results of operations, business and financial condition.

The unaudited pro forma condensed combined financial statements included in this Proxy Statement are presented for illustrative purposes only and may not be an indication of our financial condition or results of operations following the completion of the Acquisition.

The unaudited pro forma condensed combined financial statements contained in this Proxy Statement as Annex A are presented for illustrative purposes only and may not be an indication of our financial condition or results of operations following the Acquisition for several reasons. The unaudited pro forma condensed combined financial statements have been derived from the historical audited financial statements of the Company and Faeth Therapeutics for the year ended December 31, 2025 and certain adjustments and assumptions have been made regarding the Company after giving effect to the Acquisition. The information upon which these adjustments and assumptions have been made is preliminary, and these kinds of adjustments and assumptions are difficult to make with accuracy. Moreover, the unaudited pro forma condensed combined financial statements do not reflect all costs that are expected to be incurred by us in connection with the Acquisition. For example, the impact of any incremental costs incurred in integrating the two companies is not reflected in the unaudited pro forma condensed combined financial statements. As a result, the actual financial condition of the combined company following the Acquisition may not be consistent with, or evident from, these unaudited pro forma condensed combined financial statements. The assumptions used in preparing the unaudited pro forma condensed combined financial statements may not prove to be accurate, and other factors may affect our financial condition following the Acquisition. For more information, please see Annex A.

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PROPOSAL NO. 1

ELECTION OF DIRECTORS

Our Board of Directors is divided into three classes and currently has six members. Each class consists, as nearly as possible, of one-third of the total number of directors, and each class has a three-year term. Vacancies on the Board may be filled only by persons elected by a majority of the remaining directors. A director elected by the Board to fill a vacancy in a class, including vacancies created by an increase in the number of directors, shall serve for the remainder of the full term of that class and until the director’s successor is duly elected and qualified.

There are two directors in the class whose term of office expires in 2026: Bob Holmen and Kristian Humer. Each of the nominees is currently a director of the Company and each nominee was previously elected by the stockholders. If elected at the Annual Meeting, these nominees will serve until the 2029 Annual Meeting and until his successor has been duly elected and qualified, or, if sooner, until his death, resignation or removal. It is the Company’s policy to invite and encourage directors and nominees for director to attend the Annual Meeting. All of the directors then in office attended the 2025 Annual Meeting of Stockholders.

Directors are elected by a plurality of the votes of the holders of shares present virtually or represented by proxy and entitled to vote on the election of directors. Accordingly, the two nominees receiving the highest number of affirmative votes will be elected. Shares represented by executed proxies will be voted, if authority to do so is not withheld, for the election of the two nominees named below. If any of the nominees becomes unavailable for election as a result of an unexpected occurrence, shares that would have been voted for that nominee may instead be voted for the election of a substitute nominee that we propose. Each person nominated for election has agreed to serve if elected. We have no reason to believe that any of the nominees will be unable to serve.

Stockholders should understand, however, that if the Required Company Stockholder Matters are approved, the effect of the approval of the director nominees named in the Director Election Proposal will be limited because the composition of the Board is expected to be reconstituted as described in this Proxy Statement. All of our current directors other than Messrs. Donenberg, Holmen and Parikh have tendered their resignations from the Board, which such resignations are conditioned upon the receipt of stockholder approval of the Required Company Stockholder Matters and will become effective two days after the date of the Annual Meeting, or June 12, 2026. The Board has appointed each of Stephen M. Hahn, M.D., Karen Vousden, Ph.D., and Saira Ramasastry to fill the vacancies created by such resignations, which such appointments are conditioned upon the effectiveness of the resignations of Messrs. Humer, Gerry and Ricks. For more information, please see

“—Director Nominees Following the Annual Meeting.”

The Nominating and Corporate Governance Committee seeks to assemble a board that, as a whole, possesses the appropriate balance of professional and industry knowledge, financial expertise and high-level management experience and capability in various areas necessary to oversee and direct the Company’s business. To that end, the Nominating and Corporate Governance Committee has identified and evaluated nominees in the broader context of the Board’s overall composition, with the goal of recruiting members who complement and strengthen the skills of other members and who also exhibit integrity, experience, judgment, commitment, skills, and a range of expertise and other qualities that the Nominating and Corporate Governance Committee views as critical to effective functioning of the Board. The brief biographies below include information, as of the date of this proxy statement, regarding the specific and particular experience, qualifications, attributes or skills of each director or nominee that led the Nominating and Corporate Governance Committee to believe that nominee should continue to serve on the Board. However, each of the members of the Nominating and Corporate Governance Committee may have a variety of reasons why he or she believes a particular person would be an appropriate nominee for the Board, and these views may differ from the views of other members.

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The following is a brief biography of each nominee for director and their ages as of April 15, 2026, along with a discussion of the specific experience, qualifications, attributes or skills of each nominee that led the Nominating and Corporate Governance Committee to recommend that person as a nominee for director.

CLASS II DIRECTORS - NOMINEES FOR ELECTION TO THE BOARD OF DIRECTORS

Bob Holmen, age 62

Bob Holmen has served as a member of our board of directors since 2017. Mr. Holmen provides legal services focused on venture capital and private equity markets to investors through his boutique law firm Investor Counsel, where he has served as a Principal since 2016. Mr. Holmen has also served as a Managing Director since 2001 and Chief Financial Officer since 2002 at Miramar Venture Partners, a venture capital firm, and as a Principal of Holmen Ventures, a strategic financial consulting firm, since 2013. Prior to Miramar, Mr. Holmen served as an Executive Officer for CoCensys, Inc., a biopharmaceutical company, and First Consulting Group, Inc., a healthcare consulting firm. Mr. Holmen received a B.S. in Electrical Engineering from Stanford University and a J.D. from University of California, Berkeley School of Law. We believe that Mr. Holmen’s education and professional background in advising companies in the biotechnology industry qualifies him to serve on our Board.

Kristian Humer, age 51

Kristian Humer has served as a member of our board of directors since July 2021. Mr. Humer has served as the Chief Financial Officer of 4D Molecular Therapeutics, Inc. since November 2025. Prior to joining 4D Molecular Therapeutics Mr. Humer served as the Chief Financial Officer of Foghorn Therapeutics Inc. from April 2024 to November 2025. Prior to Foghorn, Mr. Humer served as the Chief Financial Officer and Chief Business Officer of Viridian Therapeutics Inc. from July 2021 to September 2023. Prior to Viridian, Mr. Humer served as Managing Director of Banking, Capital Markets and Advisory for the Global Healthcare team at Citigroup Inc., from 2017 to July 2021, where he helped lead the firm’s investment banking advisory engagements for small- and mid-sized biopharma and select large cap pharmaceutical companies. He previously served in a number of roles at Citigroup Inc., including Director, Healthcare Investment Banking from 2014 to 2016, Vice President, Healthcare Investment Banking from 2011 to 2013 and Associate, Healthcare Investment Banking in 2010. Prior to joining Citigroup Inc., Mr. Humer served as Vice President and Associate in the Investment Banking Division for the Global Healthcare team at Lehman Brothers, Inc. from 2007 to 2009. Mr. Humer started his career serving positions of increasing responsibility in the investment banking and private banking divisions of UBS AG and Merrill Lynch (a Bank of America company). He received an MBA from the Fuqua School of Business at Duke University and a B.A. (Hons) in Accounting & Economics from the University of Reading, United Kingdom. We believe that Mr. Humer’s experience in the biopharmaceutical industry and his years of investment banking and leadership experience qualify him to serve on our Board.

THE BOARD OF DIRECTORS RECOMMENDS

A VOTE “FOR” EACH NAMED NOMINEE.

CLASS III DIRECTORS CONTINUING IN OFFICE UNTIL THE 2027 ANNUAL MEETING

Christopher W. Gerry, age 46

Christopher W. Gerry is the President and General Counsel of the Company. Mr. Gerry has served as the Company’s General Counsel since July 2022 and was appointed President and Principal Executive Officer in November 2025 in connection with the Company’s leadership transition. Prior to joining the Company in July 2022, he served in roles of increasing responsibility, most recently as Vice President and Deputy General Counsel, at AVROBIO, Inc., a publicly traded biotechnology company, from November 2019 to July 2022. Prior to that, Mr. Gerry was an associate at Cooley LLP from September 2013 to October 2019, where he represented life sciences companies in a wide variety of matters. He received a B.A. from Dickinson College and earned his

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J.D. from Boston University School of Law. We believe Mr. Gerry’s experience in the life sciences industry as well as leading our company as the President and General Counsel qualifies him to serve on our Board. If the Required Company Stockholder Matters are approved, Mr. Gerry is expected to serve as the Company’s General Counsel, effective immediately following the Annual Meeting and will no longer serve as President.

Thomas Ricks, age 73

Thomas Ricks has served as a member of our board of directors since 2015. Mr. Ricks served as former Chief Investment Officer of H&S Ventures, LLC, a Forbes 150 family office, from 2001 until his retirement in 2018. Prior to his service, Mr. Ricks served as Chief Executive Officer of The University of Texas Investment Management Company from 1996 to 2001. Mr. Ricks has been a director of Ovintiv, Inc. since 2019 and currently serves as Chair of the Human Resources and Compensation Committee, and on the Corporate Responsibility and Governance Committee. He was a director of Newfield Exploration Company from 1992 to 2019 and most recently served as Chair of its Audit Committee. Mr. Ricks also served on the boards of several privately-held companies; BDM International (acquired by TRW), LifeCell Corporation, and Argus Pharmaceuticals. Mr. Ricks is a former director of the Ocean Institute, and a former member of the Investment Committees for St. David’s Foundation and the University of California – Irvine Foundation. Mr. Ricks received a B.A. in Economics from Trinity College and an M.B.A. from the University of Chicago. We believe Mr. Ricks’ extensive experience as a director of public and private companies in the healthcare industry qualifies him to serve on our Board.

CLASS I DIRECTORS CONTINUING IN OFFICE UNTIL THE 2028 ANNUAL MEETING

Phillip B. Donenberg, age 65

Phillip Donenberg has served as a member of our board of directors since February 2026. He has served as a member of the board of directors, member of the compensation committee and chairman of the audit committee of Taysha Gene Therapies, Inc., a publicly traded biotechnology company, since August 2020, and as a member of the board of directors and chairman of the audit committee of Tectonic Therapeutic, Inc. (formerly AVROBIO, Inc.), a publicly traded biotechnology company, since June 2018. He served as Senior Vice President and Chief Financial Officer of Jaguar Gene Therapy, LLC from February 2020 to March 2023. Previously, Mr. Donenberg served as Chief Financial Officer and Senior Vice President of Assertio Therapeutics, Inc., a publicly traded biotechnology company. He served as Senior Vice President and Chief Financial Officer of AveXis, Inc., a publicly traded biotechnology company, from 2017 to June 2018, and as Vice President, Corporate Controller from 2016 to 2017. Mr. Donenberg earned a B.S. in accountancy from the University of Illinois Champaign-Urbana College of Business and is a Certified Public Accountant. We believe Mr. Donenberg’s extensive experience as a director of public companies in the biotech industry qualifies him to serve on our Board.

Anand Parikh, age 40

Anand Parikh is the Chief Operating Officer of our Company. Prior to the closing of the Acquisition in February 2026, Mr. Parikh served as the Chief Executive Officer, Co-Founder and member of the board of directors of Faeth since its inception in April 2019. Prior to co-founding Faeth, Mr. Parikh served in multiple executive roles at Virta Health beginning in May 2015, including General Counsel, Head of Finance and Head of Human Resources. Earlier in his career, Mr. Parikh was a Corporate Associate at Morrison & Foerster LLP, where he advised emerging growth companies and investors on corporate transactions, including financings and mergers and acquisitions. Mr. Parikh holds a J.D. from New York University School of Law and a B.A. in Political Science from the University of Michigan. We believe that Mr. Parikh’s perspective and deep experience in the biotechnology industry, as well as his experience serving as our Chief Operating Officer and previously leading Faeth as its Chief Executive Officer, qualifies him to serve on our Board. Mr. Parikh is expected to be appointed as our Chief Executive Officer if the Required Company Stockholder Matters are approved, effective immediately following the Annual Meeting.

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DIRECTOR NOMINEES FOLLOWING THE ANNUAL MEETING

On April 10, 2026, each of our directors other than Messrs. Donenberg, Holmen and Parikh tendered their resignations from the Board, which such resignations are conditioned upon the receipt of stockholder approval of the Required Company Stockholder Matters and will become effective two days after the date of the Annual Meeting, or June 12, 2026. The Board has appointed each of the below director candidates to fill the vacancies created by such resignations, which such appointments are conditioned upon the effectiveness of the resignations of Messrs. Humer, Gerry and Ricks.

Stephen M. Hahn, age 66

Stephen M. Hahn, M.D., has served as the Chief Executive Officer of Nucleus RadioPharma, Inc., a radiopharmaceutical contract development and manufacturing organization, since July 2025, and he has served on its board of directors since May 2025. He has also served as Principal at Rubrum Advising, a healthcare consulting firm, since January 2025. From November 2021 to August 2025, Dr. Hahn served as Chief Executive Officer of Harbinger Health, a cancer diagnostics biotechnology company, and CEO-Partner at Flagship Pioneering, a life sciences venture capital company, where he also served as Chief Medical Officer of Flagship Pioneering’s Preemptive Health and Medicine Initiative from May 2021 to November 2021. Dr. Hahn currently serves as CEO Emeritus of Harbinger Health. From December 2019 to January 2021, Dr. Hahn served as the 24th Commissioner of Food and Drugs at the U.S. Food and Drug Administration. Prior to that, Dr. Hahn served in various roles at MD Anderson Cancer Center from January 2015 to December 2019, including most recently as Chief Medical Executive from June 2018 to December 2019. Dr. Hahn served on the board of directors of Faeth from October 2024 until the Closing of the Acquisition in February 2026. Dr. Hahn earned his M.D. from Temple University and received his B.A. in Biology from Rice University. He was an internal medicine resident at the University of California San Francisco before completing a fellowship and residency at the National Cancer Institute in Bethesda, Maryland. We believe that Dr. Hahn’s extensive experience in the healthcare industry, particularly his regulatory expertise, qualify him to serve on our Board. Dr. Hahn is expected to serve as a Class III director.

Saira Ramasastry, age 50

Saira Ramasastry has served as Managing Partner of Life Sciences Advisory, LLC, a company that she founded to provide strategic advice, business development solutions and innovative financing strategies for the life sciences industry in 2009. From 1999 to 2009, Ms. Ramasastry was an investment banker with Merrill Lynch & Co., Inc., an investment management company, where she helped establish the biotechnology practice and was responsible for origination of mergers and acquisitions, strategic and capital markets transactions. Prior to joining Merrill Lynch, she served as a financial analyst in the mergers and acquisitions group at Wasserstein Perella & Co., an investment banking firm, from 1997 to 1998. Ms. Ramasastry has served on the boards of directors of Day One Biopharmaceuticals, Inc. since 2021 (which has entered into a definitive agreement to be acquired by Servier S.A.S.), Mirum Pharmaceuticals, Inc. since 2022, and Vir Biotechnology, Inc. since September 2019, each a publicly traded biotechnology company, as well as Glenmark Pharmaceuticals, Ltd., a BSE and NSE-traded pharmaceuticals company, since 2019. She previously served on the boards of directors of several U.S. publicly traded companies, including: Sangamo Therapeutics, Inc., a biotechnology company, from 2012 to 2022; and Akouos, Inc., a biotechnology company, from 2020 until it was acquired by Eli Lilly and Company in 2022. Ms. Ramasastry received her B.A. in economics with honors and distinction and an M.S. in management science and engineering from Stanford University, as well as an M. Phil. in management studies from the University of Cambridge, where she is also a guest lecturer for the Bioscience Enterprise Programme. Ms. Ramasastry is also a Health Innovator Fellow of the Aspen Institute and a member of the Aspen Global Leadership Network. We believe that Ms. Ramasastry’s extensive experience in global healthcare investment banking and strategic advisory consulting in the life sciences industry qualify her to serve on our Board. Ms. Ramasastry is expected to serve as a Class III director.

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Karen Vousden, age 68

Karen Vousden, Ph.D. is a cancer biologist who has been recognized for her work on the regulation and function of the p53 tumor suppressor protein. She co-founded Faeth in April 2019. Dr. Vousden has served as Principal Group Leader of The Francis Crick Institute since February 2017. From 2016 to 2022, she served as the Chief Scientist of Cancer Research UK and was director of the Beatson Institute of Cancer Research from 2002 to 2016. Dr. Vousden has served on the board of directors of Bristol Myers Squibb Company, a publicly traded biopharmaceutical company, since 2018, where she is a member of the Science and Technology Committee and the Compensation and Management Development Committee. Dr. Vousden has been elected as a Fellow of the Royal Society, the Royal Society of Edinburgh, the Academy of Medical Sciences, EMBO, the European Academy of Sciences, the American Association of Cancer Research and the American Academy of Arts and Sciences, and as a Foreign Associate of the U.S. National Academy of Sciences. Dr. Vousden received her Ph.D. in genetics from Queen Mary College at the University of London. We believe that Dr. Vousden’s expertise as a cancer biologist, her public company board experience and her experience as a co-founder of Faeth qualify her to serve on our Board. Dr. Vousden is expected to serve as a Class II director.

INFORMATION REGARDING THE BOARD OF DIRECTORS AND CORPORATE GOVERNANCE

INDEPENDENCE OF THE BOARD OF DIRECTORS

Our Board of Directors has undertaken a review of the independence of the directors and considered whether any director has a material relationship with us that could compromise his or her ability to exercise independent judgment in carrying out his or her responsibilities. Based upon information requested from and provided by each director concerning such director’s background, employment and affiliations, including family relationships, our Board of Directors determined that all of our directors except for Messrs. Parikh and Gerry, representing four of our six directors, are “independent directors” as defined under current rules and regulations of the SEC and the listing standards of the Nasdaq Stock Market. In addition, our Board of Directors determined that (i) James Peyer and William Ringo , who each served on the Board during 2025 but are no longer on the Board, were “independent” during the period he served on the Board and (ii) John Celebi, who served on the Board during 2025 but is no longer on the Board, was not independent due to his employment as our former Chief Executive Officer.

Further, based upon information requested from and provided by each of Drs. Hahn and Vousden and Ms. Ramasastry concerning such individual’s background, employment and affiliations, including family relationships, our Board of Directors determined that all of such directors are “independent directors” as defined under current rules and regulations of the SEC and the listing standards of the Nasdaq Stock Market, other than Mr. Parikh due to his employment as our Chief Operating Officer. In making these determinations, our Board of Directors considered the current and prior relationships that each non-employee director or director candidate has with our company and all other facts and circumstances that our Board of Directors deemed relevant in determining their independence. There are no family relationships among any of our directors or executive officers.

BOARD LEADERSHIP STRUCTURE

The Board of Directors of the Company has a Chairman, Mr. Holmen, who has authority, among other things, to call and preside over Board meetings, to set meeting agendas and to determine materials to be distributed to the Board. Accordingly, the Board Chairman has substantial ability to shape the work of the Board.

Prior to the Acquisition Transactions, the Company maintained separate Board Chairman and Chief Executive Officer positions. The Board has believed that this separation reinforces the independence of the Board in its oversight of the business and affairs of the Company and creates an environment more conducive to objective evaluation of management’s performance.

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If the Required Company Stockholder Matters are approved, we expect that Mr. Parikh will serve as our Chairman and Chief Executive Officer. The Board believes that combining these roles under Mr. Parikh will be the appropriate leadership structure for the Company at that time. Following the closing of the Acquisition Transactions, the Company is undertaking a significant integration of operations, personnel, and strategic priorities. The Board believes that Mr. Parikh’s service in the combined role during this period will foster unified leadership, enable more effective decision-making, and ensure close alignment between the Board and management as the Company executes on its post-acquisition strategy.

The Board recognizes the importance of strong independent oversight and believes that the Board’s composition, committee structure, and governance practices will provide effective independent checks on management. All members of the Board’s Audit Committee, Compensation Committee, and Nominating and Corporate Governance Committee are expected to be independent directors. The Board will continue to evaluate its leadership structure on an ongoing basis and may determine that separating the roles of Chairman and Chief Executive Officer or appointing a Lead Independent Director is advisable as the Company’s needs evolve.

ROLE OF THE BOARD IN RISK OVERSIGHT

Risk is inherent with every business, and we face a number of risks, including strategic, financial, business and operational, legal and compliance, cybersecurity and reputational. One of the key functions of our Board of Directors is informed oversight of our risk management process. Our Board of Directors does not have a standing risk management committee, but rather administers this oversight function directly through the Board of Directors as a whole, as well as through various standing committees of our Board of Directors that address risks inherent in their respective areas of oversight. In particular, our Board of Directors is responsible for monitoring and assessing strategic risk exposure and our Audit Committee has the responsibility to consider and discuss our major financial risk exposures and the steps our management has taken to monitor and control these exposures, including guidelines and policies to govern the process by which risk assessment and management is undertaken. The Audit Committee also monitors compliance with legal and regulatory requirements. Our Nominating and Corporate Governance Committee monitors the effectiveness of our corporate governance guidelines, including whether they are successful in preventing illegal or improper liability-creating conduct. Our Compensation Committee assesses and monitors whether any of our compensation policies and programs has the potential to encourage excessive risk-taking. It is the responsibility of the committee chairs to report findings regarding material risk exposures to the Board as quickly as possible. The Board Chairman coordinates between the Board and management with regard to the determination and implementation of responses to any problematic risk management issues.

MEETINGS OF THE BOARD OF DIRECTORS

The Board of Directors met seven times during the last fiscal year. Each Board member attended 75% or more of the aggregate number of meetings of the Board and of the audit, compensation and nominating and corporate governance committees on which he or she served, held during the portion of the last fiscal year for which he or she was a director or committee member.

As required under applicable Nasdaq listing standards, during the last fiscal year, the Company’s independent directors met four times in regularly scheduled executive sessions at which only independent directors were present.

INFORMATION REGARDING COMMITTEES OF THE BOARD OF DIRECTORS

The Board has three committees: an Audit Committee, a Compensation Committee and a Nominating and Corporate Governance Committee. The following table provides membership and the number of meetings for the year ended December 31, 2025 for each of the Board committees:

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On February 13, 2026, the Board of Directors appointed Christopher W. Gerry and Phillip B. Donenberg as new directors, effective immediately. On February 17, 2026, effective immediately after the First Effective Time (as defined in the Merger Agreement), the Board of Directors appointed Anand Parikh as a new director and also appointed Mr. Donenberg as a member of the Audit Committee.

If the Required Company Stockholder Matters are approved, and the changes described above in “—Director Nominees Following the Annual Meeting” are implemented, we expect our committees to be reconstituted as follows:

Below is a description of each committee of the Board of Directors. Each of the committees has authority to engage legal counsel or other experts or consultants, as it deems appropriate to carry out its responsibilities. The Board of Directors has determined that each current member of each committee meets the applicable Nasdaq rules and regulations regarding “independence” and each current member is free of any relationship that would impair his or her individual exercise of independent judgment with regard to the Company.

Audit Committee

The Audit Committee of the Board of Directors was established by the Board in accordance with Section 3(a)(58)(A) of the Exchange Act to oversee the Company’s corporate accounting, disclosure controls and procedures and financial reporting processes and audits of its financial statements. The Audit Committee is currently composed of four directors: Thomas Ricks, Kristian Humer, Bob Holmen and Phillip Donenberg. Thomas Ricks serves as the Chair of the Audit Committee. The Audit Committee met four times during 2025. The Board has adopted a written Audit Committee charter that is available to stockholders on our website at www.senseibio.com.

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The Board of Directors reviews the Nasdaq listing standards definition of independence for Audit Committee members on an annual basis and has determined that all current and proposed members of our Audit Committee are independent, as independence is currently defined in Rule 5605(c)(2)(A)(i) and (ii) of the Nasdaq listing standards. The Board of Directors has also determined that Mr. Ricks and Mr. Donenberg each qualify as an “audit committee financial expert,” as defined in applicable SEC rules. The Board made a qualitative assessment of each of Mr. Ricks’ and Donenberg’s level of knowledge and experience based on a number of factors, including, for each of Mr. Ricks and Mr. Donenberg, their respective formal education and experience as a chief financial officer for public reporting companies.

The principal duties and responsibilities of our Audit Committee include:

Report of the Audit Committee of the Board of Directors

The Audit Committee has reviewed and discussed the audited financial statements for the year ended December 31, 2025 with management of the Company. The Audit Committee has discussed with the independent registered public accounting firm the matters required to be discussed by Auditing Standard No. 1301, Communications with Audit Committees, as adopted by the Public Company Accounting Oversight Board (“PCAOB”). The Audit Committee has also received the written disclosures and the letter from the independent registered public accounting firm required by applicable requirements of the PCAOB regarding the independent accountants’ communications with the Audit Committee concerning independence, and has discussed with the independent registered public accounting firm the accounting firm’s independence. Based on the foregoing, the Audit Committee has recommended to the Board of Directors that the audited financial statements be included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2025.

Thomas Ricks, Chair

Kristian Humer

Bob Holmen

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Phillip B. Donenberg

Compensation Committee

The Compensation Committee is composed of three directors: Messrs. Ricks, Humer and Holmen. Mr. Holmen serves as the Chair of the Compensation Committee. Each of the committee members are non-employee directors, as defined in Rule 16b-3 promulgated under the Exchange Act. Our Board of Directors has determined that each of the current and proposed committee members are “independent” as defined under the applicable Nasdaq listing standards, including the standards specific to members of a compensation committee. The Compensation Committee met twice during 2025. The Board has adopted a written Compensation Committee charter that is available to stockholders on our website at www.senseibio.com.

The principal duties and responsibilities of our Compensation Committee include:

Compensation Committee Processes and Procedures

Typically, the Compensation Committee meets an average of once every quarter and with greater frequency if necessary. The agenda for each meeting is usually developed by the Chair of the Compensation Committee, in consultation with our Chief Executive Officer. The Compensation Committee meets regularly in executive session. However, from time to time, various members of management and other employees as well as outside advisors or consultants may be invited by the Compensation Committee to make presentations, to provide financial or other background information or advice or to otherwise participate in Compensation Committee meetings. Our Compensation Committee typically reviews and discusses management’s proposed compensation with the Chief Executive Officer for all executives other than the Chief Executive Officer. The Chief Executive Officer may not participate in, or be present during, any deliberations or determinations of the Compensation Committee regarding his compensation or individual performance objectives. The charter of the Compensation Committee grants the Compensation Committee full access to all books, records, facilities and personnel of the Company. In addition, under the charter, the Compensation Committee has the authority to obtain, at the expense of the Company, advice and assistance from compensation consultants and internal and external legal, accounting or other advisors and other external resources that the Compensation Committee considers necessary or appropriate in the performance of its duties. The Compensation Committee has direct responsibility for the oversight of the work of any consultants or advisers engaged for the purpose of advising the Compensation

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Committee. In particular, the Compensation Committee has the sole authority to retain, in its sole discretion, compensation consultants to assist in its evaluation of executive and director compensation, including the authority to approve the consultant’s reasonable fees and other retention terms. Under the charter, the Compensation Committee may select, or receive advice from, a compensation consultant, independent legal counsel or other adviser to the Compensation Committee, other than in-house legal counsel and certain other types of advisers, only after taking into consideration six factors, prescribed by the SEC and Nasdaq, that bear upon the adviser’s independence.

During the past fiscal year, after taking into consideration the six factors prescribed by the SEC and Nasdaq described above, the Compensation Committee engaged Alpine Rewards as independent compensation consultants. Our Compensation Committee identified Alpine Rewards based on its general reputation in the industry. The Compensation Committee requested that Alpine Rewards:

Nominating and Corporate Governance Committee

The Nominating and Corporate Governance Committee is composed of three directors: Messrs. Holmen, Ricks and Humer. Mr. Humer serves as Chair of the Nominating and Corporate Governance Committee. All current and proposed members of the Nominating and Corporate Governance Committee are independent (as independence is currently defined in Rule 5605(a)(2) of the Nasdaq listing standards). The Nominating and Corporate Governance Committee did not meet during 2025 and instead acted by unanimous written consent. The Board has adopted a written Nominating and Corporate Governance Committee charter that is available to stockholders on the Company’s website at www.senseibio.com.

The Nominating and Corporate Governance Committee’s responsibilities include:

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The Nominating and Corporate Governance Committee believes that candidates for director should have certain minimum qualifications, including the ability to read and understand basic financial statements, being over 21 years of age and having the highest personal integrity and ethics. The Nominating and Corporate Governance Committee also intends to consider such factors as possessing relevant expertise upon which to be able to offer advice and guidance to management, having sufficient time to devote to the affairs of the Company, demonstrated excellence in his or her field, having the ability to exercise sound business judgment and having the commitment to rigorously represent the long-term interests of the Company’s stockholders. However, the Nominating and Corporate Governance Committee retains the right to modify these qualifications from time to time. Candidates for director nominees are reviewed in the context of the current composition of the Board, the operating requirements of the Company and the long-term interests of stockholders. In conducting this assessment, the Nominating and Corporate Governance Committee typically considers a range of age, skills and such other factors as it deems appropriate, given the current needs of the Board and the Company, to maintain a balance of knowledge, experience and capability. Diversity is one of a number of factors, however, that the committee takes into account in identifying nominees, and the Nominating and Corporate Governance Committee believes that it is essential that the board members represent diverse viewpoints.

In the case of incumbent directors whose terms of office are set to expire, the Nominating and Corporate Governance Committee reviews these directors’ overall service to the Company during their terms, including the number of meetings attended, level of participation, quality of performance and any other relationships and transactions that might impair the directors’ independence. In the case of new director candidates, the Nominating and Corporate Governance Committee also determines whether the nominee is independent for Nasdaq purposes, which determination is based upon applicable Nasdaq listing standards, applicable SEC rules and regulations and the advice of counsel, if necessary. The Nominating and Corporate Governance Committee then uses its network of contacts to compile a list of potential candidates, but may also engage, if it deems appropriate, a professional search firm. The Nominating and Corporate Governance Committee conducts any appropriate and necessary inquiries into the backgrounds and qualifications of possible candidates after considering the function and needs of the Board. The Nominating and Corporate Governance Committee meets to discuss and consider the candidates’ qualifications and then selects a nominee for recommendation to the Board by majority vote.

The Nominating and Corporate Governance Committee will consider director candidates recommended by stockholders. The Nominating and Corporate Governance Committee does not intend to alter the manner in which it evaluates candidates, including the minimum criteria set forth above, based on whether or not the candidate was recommended by a stockholder. Stockholders who wish to recommend individuals for consideration by the Nominating and Corporate Governance Committee to become nominees for election to the Board may do so by delivering a written recommendation to the Nominating and Corporate Governance Committee at the following address: Secretary, Sensei Biotherapeutics, Inc., 1405 Research Blvd, Suite 125, Rockville, Maryland 20850, at least 90 days, but not more than 120 days, prior to the anniversary date of the mailing of our proxy statement for the preceding year’s annual meeting of stockholders. Submissions must include: (1) the name and address of the Company stockholder on whose behalf the submission is made; (2) the number of Company shares that are owned beneficially by such stockholder as of the date of the submission; (3) the full name, age, business address and residence address of the proposed candidate; (4) a description of the proposed candidate’s principal occupation or employment; (5) the class and number of shares of each class of capital stock of the corporation which are owned of record and beneficially by such proposed candidate; and (6) such additional information as is required by our bylaws. Each submission must be accompanied by the written consent of the proposed candidate to be named as a nominee and to serve as a director if elected.

STOCKHOLDER COMMUNICATIONS WITH THE BOARD OF DIRECTORS

The Board of Directors has adopted a formal process by which stockholders may communicate with the Board of Directors or any of its directors. Stockholders who wish to communicate with the Board of Directors may do so by sending written communications addressed to the Board of Directors or the director in care of Sensei

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Biotherapeutics, Inc., 1405 Research Blvd, Suite 125, Rockville, Maryland 20850, Attn: Secretary. Each communication must set forth the name and address of the stockholder on whose behalf the communication is sent and the number and class of shares of our stock that are owned beneficially by the stockholder as of the date of the communication.

These communications will be reviewed by our Secretary, who will determine whether they should be presented to the Board of Directors. The purpose of this screening is to allow the Board of Directors to avoid having to consider communications that contain advertisements or solicitations or are unduly hostile, threatening or similarly inappropriate. All communications directed to the audit committee in accordance with our Open Door Policy for Reporting Complaints Regarding Accounting and Auditing Matters that relate to questionable accounting or auditing matters involving the Company will be promptly and directly forwarded to the Audit Committee.

Any interested person may communicate directly with the non-management directors. Persons interested in communicating directly with the non-management directors regarding their concerns or issues may do so by addressing correspondence to a particular director, or to the non-management directors generally, in care of Sensei Biotherapeutics, Inc., 1405 Research Blvd, Suite 125, Rockville, Maryland 20850. If no particular director is named, letters will be forwarded, depending upon the subject matter, to the chair of the Audit, Compensation, Nominating and Corporate Governance Committee.

CODE OF BUSINESS CONDUCT AND ETHICS

We have adopted a Code of Business Conduct and Ethics (the “Code of Conduct”) applicable to all of our employees, executive officers and directors. The Code of Conduct is available on our website at www.senseibio.com. The Nominating and Corporate Governance Committee is responsible for overseeing the Code of Conduct and must approve any waivers of the Code of Conduct for executive officers and directors. If we make any substantive amendments to the Code of Conduct or grants any waiver from a provision of the Code of Conduct to any executive officer or director, we will promptly disclose the nature of the amendment or waiver on our website.

CORPORATE GOVERNANCE GUIDELINES

In connection with our initial public offering, the Board documented the governance practices followed by the Company by adopting Corporate Governance Guidelines to assure that the Board will have the necessary authority and practices in place to review and evaluate our business operations as needed and to make decisions that are independent of our management. The Corporate Governance Guidelines are also intended to align the interests of directors and management with those of our stockholders. The Corporate Governance Guidelines set forth the practices the Board intends to follow with respect to board composition and selection, board meetings and involvement of senior management, Chief Executive Officer performance evaluation and succession planning, and board committees and compensation. The Nominating and Corporate Governance Committee regularly reviews the Corporate Governance Guidelines, seeks advice and recommendations from outside advisors, and considers corporate governance trends and best practices in our industry.

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PROPOSAL NO. 2

RATIFICATION OF SELECTION OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

The Audit Committee of the Board has selected Deloitte & Touche LLP as the Company’s independent registered public accounting firm for the year ending December 31, 2026 and has further directed that management submit the selection of its independent registered public accounting firm for ratification by the stockholders at the Annual Meeting. Deloitte & Touche LLP has audited the Company’s financial statements since 2016. Representatives of Deloitte & Touche LLP are expected to be present at the Annual Meeting. They will have an opportunity to make a statement if they so desire and will be available to respond to appropriate questions.

Neither the Company’s Bylaws nor other governing documents or law require stockholder ratification of the selection of Deloitte & Touche LLP as the Company’s independent registered public accounting firm. However, the Audit Committee of the Board is submitting the selection of Deloitte & Touche LLP to the stockholders for ratification as a matter of good corporate practice. If the stockholders fail to ratify the selection, the Audit Committee of the Board will reconsider whether or not to retain that firm. Even if the selection is ratified, the Audit Committee of the Board in its discretion may direct the appointment of different independent auditors at any time during the year if they determine that such a change would be in the best interests of the Company and its stockholders.

The affirmative vote of the holders of a majority of the shares present virtually or represented by proxy and entitled to vote on the matter at the Annual Meeting will be required to ratify the selection of Deloitte & Touche LLP.

FEES FOR SERVICES PROVIDED BY THE INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

The following table represents aggregate fees for professional services rendered to the Company for the years ended December 31, 2025 and 2024 by Deloitte & Touche LLP, the Company’s independent registered public accounting firm.

There were no other fees for the years ended December 31, 2025 and 2024.

PRE-APPROVAL POLICIES AND PROCEDURES

The Audit Committee has adopted a policy and procedures for the pre-approval of audit and non-audit services rendered by the Company’s independent auditors, Deloitte & Touche LLP. The Audit Committee generally pre-approves specified services in the defined categories of audit services, audit-related services and tax services

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up to specified amounts. Pre-approval may also be given as part of the Audit Committee’s approval of the scope of the engagement of the independent auditor or on an individual, explicit, case-by-case basis before the independent auditor is engaged to provide each service. The pre-approval of services may be delegated to one or more of the Audit Committee’s members, but the decision must be reported to the full Audit Committee at its next scheduled meeting.

All of the services of Deloitte & Touche LLP for the years ended December 31, 2025 and 2024 described above were pre-approved in accordance with the Audit Committee Pre-Approval Policy.

THE BOARD OF DIRECTORS RECOMMENDS

A VOTE “FOR” PROPOSAL NO. 2.

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PROPOSAL NO. 3

APPROVAL OF ISSUANCE OF COMMON STOCK UPON CONVERSION OF SERIES B PREFERRED STOCK, WHICH WILL (A) REPRESENT MORE THAN 20% OF THE SHARES OF COMMON STOCK OUTSTANDING AND (B) RESULT IN THE CHANGE OF CONTROL OF THE COMPANY PURSUANT TO NASDAQ LISTING RULES 5635(A) AND 5635(B), RESPECTIVELY

Overview

As described above, we issued 10,497.0980 shares of Series B Preferred Stock and 14,440.395 shares of Series B Preferred Stock in the Acquisition and the 2026 Private Placement, respectively, each of which is convertible into 1,000 shares of common stock, subject to certain conditions described below. The Series B Preferred Stock is intended to have rights that are generally equivalent to our common stock, provided that the Series B Preferred Stock does not have the right to vote on most matters (including the election of directors or any proposals herein). The shares of Series B Preferred Stock will automatically convert into an aggregate of 24,937,493 shares of common stock upon the third business day following receipt of approval of the Required Company Stockholder Matters in accordance with Nasdaq listing rules up to the beneficial ownership limitations set by each holder; provided that such beneficial ownership limitations may be waived by each holder of Series B Preferred Stock at any time following the approval by Nasdaq of the Nasdaq Listing Application and approval of the Required Company Stockholder Matters.

Nasdaq Listing Rule 5110 requires that the Company submit, and Nasdaq approve, the Nasdaq Listing Application prior to the approval by our stockholders of a change of control pursuant to Nasdaq Listing Rule 5635(b). The approval being sought in this Proposal No. 3, along with the filing of the Nasdaq Listing Application with Nasdaq, is intended to satisfy this obligation of the Company.

With respect to the Nasdaq Listing Application and compliance with the initial listing standards of the Nasdaq Capital Market, Annex A of this proxy statement sets forth certain unaudited pro forma financial information for the Company as of and for the year ended December 31, 2025, after giving effect to the entrance into the Acquisition Transactions and the automatic conversion of all of the Series B Preferred Stock into common stock following stockholder approval of the Required Company Stockholder Matters.

Shares Issuable Upon Conversion

Set forth below is a table summarizing the issued and outstanding shares of Series B Preferred Stock and the number of shares of common stock that are potentially issuable upon conversion of the Series B Preferred Stock. The sale into the public market of the underlying common stock could materially and adversely affect the market price of our common stock.

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Description of Series B Preferred Stock

The following summary of the terms of the Series B Preferred Stock is not complete and is qualified in its entirety by the provisions of the Certificate of Designation, which is filed as Exhibit 3.1 to our Current Report on Form 8-K, filed with the SEC on February 18, 2026.

Conversion. Following stockholder approval of the Required Company Stockholder Matters, effective as of 5:00 p.m. (Eastern time) on the third business day after the date on which such stockholder approval is received, each outstanding share of Series B Preferred Stock will automatically convert into 1,000 shares of common stock, subject to certain beneficial ownership limitations, including that a holder of Series B Preferred Stock is prohibited from converting shares of Series B Preferred Stock into shares of Common Stock if, as a result of such conversion, such holder, together with its affiliates, would beneficially own more than a specified percentage (initially set by the holder to a number up between 4.99% and 19.99% and thereafter adjusted) of the total number of shares of common stock issued and outstanding immediately after giving effect to such conversion; provided that such beneficial ownership limitations may be waived by each holder of Series B Preferred Stock at any time following the approval by Nasdaq of the Nasdaq Listing Application and approval of the Required Company Stockholder Matters upon notice to the Company. We intend to seek a waiver of such beneficial ownership limitations from our holders of Series B Preferred Stock to be effective following the approval by our stockholders of the Required Company Stockholder Matters. If any shares of Series B Preferred Stock continue to be outstanding following such automatic conversion due to a beneficial ownership limitation that was not waived, such shares of Series B Preferred Stock will be convertible at the option of the holder, subject to such beneficial ownership limitations.

Voting Rights. Except as otherwise required by the Certificate of Designation or the General Corporation Law of the State of Delaware (“DGCL”), the Series B Preferred Stock does not have voting rights. However, as long as any shares of Series B Preferred Stock are outstanding, we will not, without the affirmative vote of the holders of a majority of the then outstanding shares of the Series B Preferred Stock, (i) alter or change adversely the powers, preferences or rights given to the Series B Preferred Stock, or alter or amend the Certificate of Designation, amend or repeal any provision of, or add any provision to, our certificate of incorporation or bylaws, or file any articles of amendment, certificate of designations, preferences, limitations and relative rights of any series of our preferred stock, in each case, if such action would adversely alter or change the preferences, rights, privileges or powers of, or restrictions provided for the benefit of the Series B Preferred Stock, regardless of whether any of the foregoing actions shall be by means of amendment to our certificate of incorporation or by merger, consolidation, recapitalization, reclassification, conversion or otherwise, (ii) issue further shares of Series B Preferred Stock or increase or decrease (other than by conversion) the number of authorized shares of Series B Preferred Stock, (iii) prior to receipt of stockholder approval of the Required Company Stockholder Matters, consummate either (A) any Fundamental Transaction (as defined in the Certificate of Designation) or (B) any merger or consolidation of the Company or any stock sale to or other business combination (including, without limitation, a reorganization, recapitalization, spin-off, share exchange or scheme of arrangement) with or into another person in which our stockholders immediately before such transaction do not hold at least a majority of our capital stock immediately after such transaction or in which the Company issues securities in such transaction that represent or are convertible into securities representing more than a majority of the voting power of the Company immediately before such transaction (a “Change of Control Transaction”), (iv) prior to receipt of stockholder approval of the Required Company Stockholder Matters, authorize or issue any class or series of stock that has powers, preferences or rights that are senior to those of the Series B Preferred Stock, (v) amend, waive or modify the Merger Agreement in any manner that would be reasonably likely to prevent, impede or materially delay the receipt of stockholder approval of the Required Company Stockholder Matters or the automatic conversion of the Series B Preferred Stock, or (vi) enter into any agreement with respect to any of the foregoing.

Cash Settlement. If, at any time after the earlier of (i) receipt of approval of the Required Company Stockholder Matters and (ii) August 17, 2026, the Company fails to deliver to the holder of shares of Series B Preferred Stock a certificate or certificates representing shares of common stock, or electronically deliver (or cause its transfer agent to electronically deliver) such shares, on or prior to the first trading day after the applicable Share Delivery

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Date (as defined in the Certificate of Designation), subject to certain limited exceptions, the Company shall, at the request of the holder of the shares of Series B Preferred Stock, pay an amount in cash by wire transfer of immediately available funds equal to the Fair Value (as defined below) of such undelivered shares, with such payment to be made within two business days from the date of request by such holder, whereupon the Company’s obligations to deliver such shares underlying the Notice of Conversion (as defined in the Certificate of Designation) shall be extinguished upon payment in full of the Fair Value of such undelivered shares. The cash settlement provisions set forth in the Certificate of Designation shall be available irrespective of the reason for the Company’s failure to timely deliver the applicable shares of Common Stock including due to the lack of obtaining the approval of the Required Company Stockholder Matters and/or the Nasdaq Listing Application. The “Fair Value” of shares shall be fixed with reference to the last reported closing sale price on the Nasdaq Capital Market, or other principal trading market on which the Company’s common stock is listed, as of the trading day immediately prior to the date on which the Notice of Conversion is delivered to the Company.

Dividends. Holders of Series B Preferred Stock are entitled to receive dividends on shares of Series B Preferred Stock equal, on an as-if-converted-to-common stock basis, and in the same form as dividends actually paid on shares of our common stock.

Liquidation and Dissolution. The Series B Preferred Stock ranks on parity with our common stock upon any liquidation, dissolution or winding-up of the Company.

Reasons for Stockholder Approval

Our common stock is listed on the Nasdaq Capital Market, and, as such, we are subject to the applicable rules of the Nasdaq Stock Market LLC, including Nasdaq Listing Rule 5635(a), which requires stockholder approval in connection with the acquisition of another company if the Nasdaq-listed company will issue more than 20% of its common stock. For purposes of Nasdaq Listing Rule 5635(a), the issuance of any common stock in the Acquisition Transactions would be aggregated together. If all shares of Series B Preferred Stock are converted into shares of our common stock (without giving effect to any beneficial ownership limitations), the shares of common stock issued upon such conversion and the shares of common stock issuable upon conversion of the assumed warrant, would constitute approximately 95.1% of our issued and outstanding stock as of the record date. Thus, in order to permit the issuance of common stock upon conversion of the Series B Preferred Stock, we must first obtain stockholder approval of this issuance.

In addition, pursuant to Nasdaq Listing Rule 5635(b), stockholder approval is required prior to the issuance of securities that will result in a “change of control” of a listing company. Nasdaq has not formally defined what constitutes a “change of control” but Nasdaq guidance provides that generally a change of control occurs when, as a result of the issuance of securities in such transaction, an investor or a group of investors would own, or have the right to acquire, 20% or more of the outstanding shares of common stock or voting power and such ownership or voting power would be the largest ownership position. In addition, Nasdaq will consider all facts and circumstances concerning a transaction, including whether there are any other relationships or agreements between a company and an investor. Additionally, under Nasdaq Listing Rule 5110(a), Nasdaq guidance suggests that a change of control could result based on changes to the voting power and/or share ownership, management and board of directors of the listing company. The Certificate of Designation permits the waiver of the 19.99% beneficial ownership limitation following approval of the Nasdaq Listing Application and the Required Company Stockholder Matters. In addition, we intend to change a majority of the Board and our executive officers following approval of the Nasdaq Listing Application and the Required Company Stockholder Matters. Although the conversion of the Series B Preferred Stock will not result in an investor beneficially owning more than 20% of our voting power, the waiver of the beneficial ownership limitations and our expected changes to the Board and management may be deemed a “change of control” by Nasdaq. Accordingly, we are seeking stockholder approval of a “change of control” under Nasdaq Listing Rules. Stockholders should note that a “change of control” as described under Nasdaq Listing Rule 5635(b) applies only with respect to the application of such rule and does not constitute a “change of control” for purposes of Delaware law, our organizational documents or any other purpose.

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Effect of Proposal No. 3

In the event that our stockholders approve this Proposal No. 3, and Proposal No. 4 is also approved, at the Annual Meeting and Nasdaq approves the Nasdaq Listing Application, the Series B Preferred Stock will become immediately convertible into shares of common stock, subject to any beneficial ownership limitations set by the holder and not waived. The issuance of our shares of common stock upon the conversion of the Series B Preferred Stock will not affect the rights or privileges of our existing stockholders, except that the economic and voting interests of each of our existing stockholders will be diluted. Although the number of shares of common stock that our existing stockholders own will not decrease, the shares of common stock owned by our existing stockholders will represent a substantially smaller percentage of our total outstanding shares of common stock after any such conversion.

In the event that our stockholders do not approve this Proposal No. 3 at the Annual Meeting, the Series B Preferred Stock will not become convertible unless and until stockholders approve of such conversion and issuance of shares of common stock for the purposes of complying with the applicable provisions of Nasdaq Listing Rule 5635. Pursuant to the Merger Agreement and the Purchase Agreement, if we fail to receive sufficient proxies to constitute a quorum or to obtain the required vote on this Proposal No. 3, we would be required to adjourn the Annual Meeting one or more times for up to 30 days per adjournment. Further, in the event that our stockholders do not approve this Proposal No. 3 at the Annual Meeting, we are required to use our reasonable best efforts to secure the approvals sought in this Proposal No. 3 as soon as practicable following the date of the Annual Meeting. We will be required to hold an annual meeting or a special meeting at least every six months to solicit and take a vote on the approvals sought in this Proposal No. 3 until such approvals are obtained. The process of continuing to hold stockholder meetings to obtain such approvals would cause us to incur significant legal expenses and could divert our management’s attention from the operation of our business. In addition, if we are unable to obtain approval of the Required Company Stockholder Matters, including this Proposal No. 3, we may be required to make significant cash settlement payments to the holders of Series B Preferred Stock who submit Notices of Conversion after August 17, 2026.

Interests of Certain Parties

In connection with the Acquisition Transactions, Anand Parikh was appointed as our Chief Operating Officer and a member of our Board. Mr. Parikh is expected to be appointed as our Chief Executive Officer if the Required Company Stockholder Matters are approved. Mr. Parikh also received shares of Series B Preferred Stock in the Acquisition that will be converted into common stock upon approval of this Proposal No. 3. In addition, as described in “Executive Officers—Expected Chief Financial Officer Following the Annual Meeting,” Brian Stephenson, Ph.D., is expected to be appointed as our Chief Financial Officer if the Required Company Stockholder Matters are approved. Separately, as described in “Proposal No. 1—Election of Directors—Director Nominees Following the Annual Meeting,” Drs. Hahn and Vousden and Ms. Ramasastry are expected to be appointed to our Board if the Required Company Stockholder Matters are approved. Drs. Hahn and Vousden, who previously served on the board of directors of Faeth Therapeutics, also received shares of Series B Preferred Stock in the Acquisition that will be converted into common stock upon approval of this Proposal No. 3. Further, in connection with the execution of the Merger Agreement, the Company and Faeth Subsidiary entered into Support Agreements with certain of our officers and directors (solely in their capacity as stockholders), representing approximately 1.5% of shares of common stock outstanding on the record date. The Support Agreements provide that, among other things, each of the parties thereto has agreed to vote or cause to be voted all of the shares of common stock beneficially owned by such stockholder in favor of Proposals Nos. 3, 4, 5 and 6 at the Annual Meeting, subject to and in accordance with the terms of the Support Agreements.

THE BOARD OF DIRECTORS RECOMMENDS

A VOTE “FOR” PROPOSAL NO. 3.

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PROPOSAL NO. 4

APPROVAL OF AMENDMENT OF THE CERTIFICATE OF INCORPORATION TO INCREASE THE NUMBER OF AUTHORIZED SHARES OF COMMON STOCK FROM 12,500,000 TO 300,000,000

The Board is requesting stockholder approval of an amendment to the Company’s Amended and Restated Certificate of Incorporation to increase the Company’s authorized number of shares of common stock from 12,500,000 shares to 300,000,000 shares. The Board of Directors has not approved an increase in the authorized shares of any class of preferred stock, including the Series B Preferred Stock. The text of the proposed amendment is set forth on Annex B to this Proxy Statement.

The additional common stock to be authorized by adoption of the amendment would have rights identical to the currently outstanding common stock of the Company. Adoption of the proposed amendment would not affect the rights of the holders of currently outstanding common stock of the Company, except for effects incidental to increasing the number of shares of the Company’s common stock available for future issuance, which would result in dilution of the earnings per share and voting rights of current holders of common stock. If the amendment is adopted, it will become effective upon filing of a Certificate of Amendment to the Company’s Amended and Restated Certificate of Incorporation with the Secretary of State of the State of Delaware.

As of the record date, April 13, 2026, there were 1,341,140 shares of common stock issued and outstanding and entitled to vote. On the record date, there were 24,937.493 shares of Series B Preferred Stock issued and outstanding; however, the Series B Preferred Stock are not entitled to vote on the matters being considered at the Annual Meeting. In addition, as of April 13, 2026, (i) an aggregate of 24,937,493 shares of common stock are issuable upon conversion of the Series B Preferred Stock, (ii) an aggregate of 311,164 shares of common stock are issuable upon exercise of outstanding stock options, (iii) 631 shares of common stock are issuable upon vesting/settlement of outstanding restricted stock units, (iv) 1,372 shares of common stock are issuable upon exercise of outstanding warrants, (v) 35,421 shares of common stock are reserved for issuance under the 2021 EIP, (vi) 72,853 shares of common stock are reserved for issuance under the 2021 ESPP and (vii) if Proposals No. 5 and No. 6 are approved, 2,983,145 and 267,198 shares of common stock, respectively, will be reserved for issuance under the 2026 Plan and the 2026 ESPP. Accordingly, as of the record date, the Company’s common stock share reserve exceeded the Company’s authorized shares of common stock by 14,200,074 shares (or 17,139,253 shares if Proposals No. 5 and No. 6 are approved). Accordingly, at present, there are not sufficient available unissued and unreserved authorized shares of our common stock to meet the needs of our business described below under “— Reasons for Stockholder Approval”.

The proposed amendment to our Certificate of Incorporation would increase the number of shares of common stock that we are authorized to issue from 12,500,000 shares of common stock to 300,000,000 shares of common stock, representing an increase of 287,500,000 shares of authorized common stock. The proposed amendment to our Amended and Restated Certificate of Incorporation would not increase the number of shares of preferred stock that we are authorized to issue. The proposed form of amendment to our Amended and Restated Certificate of Incorporation to effect the Authorized Share Increase Proposal is attached as Annex B to this proxy statement.

Reasons for Stockholder Approval

As described in greater detail under Proposal No. 3, in connection with the Acquisition of Faeth Therapeutics completed on February 17, 2026, we issued 10,497.0980 shares of Series B Preferred Stock to the former stockholders of Faeth HoldCo, and, on February 20, 2026, we issued 14,440.395 shares of Series B Preferred Stock in the 2026 Private Placement for aggregate gross proceeds of approximately $200 million, each share of which is convertible into 1,000 shares of common stock. Subject to the receipt of stockholder approval of the Required Company Stockholder Matters, each outstanding share of Series B Preferred Stock will automatically convert into 1,000 shares of common stock, subject to certain beneficial ownership limitations established by each holder.

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The shares of Series B Preferred Stock will automatically convert into an aggregate of 24,937,493 shares of common stock upon the third business day following receipt of approval of the Required Company Stockholder Matters in accordance with Nasdaq listing rules and up to the beneficial ownership limitations set by each holder. In addition, following the conversion of the shares of Series B Preferred Stock, a warrant we assumed in the Acquisition that is currently exercisable for 2.1020 shares of Series B Preferred Stock will become exercisable for 2,102 shares of common stock. Because our certificate of incorporation currently authorizes only 12,500,000 shares of common stock, we do not have a sufficient number of authorized shares of common stock to permit the conversion of all of the outstanding shares of Series B Preferred Stock into common stock. The approval of this Proposal No. 4 is therefore necessary to permit the conversion of the Series B Preferred Stock into common stock as contemplated by the Certificate of Designation, the Merger Agreement and the Purchase Agreement.

In addition to providing sufficient shares to permit the conversion of the Series B Preferred Stock, the additional authorized shares of common stock will be available for issuance from time to time at the discretion of our Board of Directors for any proper corporate purpose, including, without limitation:

Except to the extent required by applicable law, regulation or the rules of the Nasdaq Stock Market, any future issuances of authorized shares of common stock may be approved by the Board of Directors without further action by our stockholders. The availability of additional authorized shares of common stock would be particularly important in the event that the Board of Directors needs to undertake any of the foregoing actions on an expedited basis, in order to avoid the time and expense of seeking stockholder approval in connection with any contemplated issuance, where such approval might not otherwise be required. Although the Board of Directors will issue common stock only when required or when the Board of Directors considers such issuance to be in our and our stockholders’ best interests, the issuance of additional common stock may, among other things, have a dilutive effect on the earnings per share (if any) and on the equity and voting rights of our existing stockholders.

Anti-Takeover and Dilutive Effects

The shares of common stock that are authorized but unissued provide the Board of Directors with flexibility to effect, among other transactions, public or private financings, including the issuance and exercise of warrants, acquisitions, stock dividends, stock splits, and the granting of equity incentive awards. However, these authorized but unissued shares may also be used by the Board of Directors, consistent with and subject to its fiduciary duties, to deter future attempts to gain control of us or make such actions more expensive and less desirable. The Authorized Share Proposal would continue to give the Board of Directors authority to issue additional shares from time to time without delay or further action by the stockholders, except as may be required by applicable law, regulation or Nasdaq listing rules.

The Authorized Share Increase is not being recommended in response to any specific effort of which we are aware to obtain control of the Company, nor does the Board of Directors have any present intent to use the authorized but unissued common stock to impede a takeover attempt. While the Authorized Share Increase may be deemed to have potential anti-takeover effects, the proposal is not prompted by any specific effort or takeover threat currently perceived by management. In addition, we do not have any plans to implement additional measures having anti-takeover effects.

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The Authorized Share Increase will increase the number of authorized shares of common stock and, as a result, the Board of Directors’ ability to issue authorized and unissued shares without further stockholder action. The issuance of additional shares of common stock may have a dilutive effect on earnings per share and relative voting power and may cause a decline in the trading price of our common stock. We could use the shares that are available for future issuance in dilutive equity financing transactions, or to oppose a hostile takeover attempt or delay or prevent changes in control or changes in or removal of management, including transactions that are favored by a majority of the stockholders or in which the stockholders might otherwise receive a premium for their shares over then-current market prices or benefit in some other manner.

In the event that stockholders approve this Proposal No. 4, and Proposal No. 3 is also approved and Nasdaq approves the Nasdaq Listing Application, the Series B Preferred Stock will become immediately convertible into shares of common stock, subject to any beneficial ownership limitations set by each holder and not waived. The issuance of shares of common stock upon the conversion of the Series B Preferred Stock will not affect the rights or privileges of our existing stockholders, except that the economic and voting interests of each of our existing stockholders will be diluted. Although the number of shares of common stock that our existing stockholders own will not decrease, the shares of common stock owned by our existing stockholders will represent a substantially smaller percentage of our total outstanding shares of common stock after any such conversion.

As a result of the Acquisition Transactions, immediately following the PIPE Closing, equityholders of the Company immediately prior to the Acquisition owned approximately 4.9% of the common stock, equityholders of Faeth Therapeutics immediately prior to the Acquisition owned approximately 40.6% of the common stock, and the Investors in the 2026 Private Placement owned approximately 54.5% of the common stock, in each case calculated on a fully-diluted, as-converted-to-common basis (and without giving effect to any beneficial ownership limitations) using the treasury stock method and based on the implied equity values of the Company and Faeth Therapeutics.

Other than the obligation to issue shares of common stock upon the conversion of the outstanding Series B Preferred Stock and shares issuable upon the exercise or settlement of outstanding stock options and restricted stock units under our existing equity plans or under the 2026 Plan and 2026 ESPP, if approved, and underlying outstanding warrants, we have no specific plan, commitment, arrangement, understanding or agreement, either oral or written, regarding the issuance of common stock subsequent to the Authorized Share Increase at this time, and we have not allocated any specific portion of the authorized shares to any particular purpose.

Consequences if Proposal No. 4 Is Not Approved

In the event that our stockholders do not approve this Proposal No. 4 at the Annual Meeting, we are required to use our reasonable best efforts to secure the approvals sought in this Proposal No. 4 as soon as practicable following the date of the Annual Meeting. Pursuant to the Merger Agreement and the Purchase Agreement, if we fail to receive sufficient proxies to constitute a quorum or to obtain the required vote on this Proposal No. 4, we would be required to adjourn the Annual Meeting one or more times for up to 30 days per adjournment. Further, we will be required to hold an annual meeting or a special meeting at least every six months to solicit and take a vote on the approvals sought in this Proposal No. 4 until such approvals are obtained. The process of continuing to hold stockholder meetings to obtain such approvals would cause us to incur significant legal expenses and could divert our management’s attention from the operation of our business. In addition, if we are unable to obtain approval of the Required Company Stockholder Matters, including this Proposal No. 4, we may be required to make significant cash settlement payments to the holders of Series B Preferred Stock who submit Notices of Conversion after August 17, 2026.

Procedure for Effecting the Authorized Share Increase

If this Proposal No. 4 is approved by our stockholders, we will promptly file the Certificate of Amendment with the Secretary of State of the State of Delaware to amend our existing Amended and Restated Certificate of Incorporation. The Authorized Share Increase will become effective upon the date of filing and acceptance of the

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Certificate of Amendment by the Secretary of State of the State of Delaware. The text of the Certificate of Amendment is set forth in Annex B to this proxy statement and is subject to modification to include such changes as may be required by the office of the Secretary of State of the State of Delaware and as the Board of Directors deems necessary and advisable to effect the Authorized Share Increase.

The description of the Certificate of Amendment set forth above is qualified in its entirety by reference to the full text of the Certificate of Amendment, which is attached as Annex B to this proxy statement.

Interests of Certain Parties

In connection with the Acquisition Transactions, Anand Parikh was appointed as our Chief Operating Officer and a member of our Board. Mr. Parikh is expected to be appointed as our Chief Executive Officer if the Required Company Stockholder Matters are approved. Mr. Parikh also received shares of Series B Preferred Stock in the Acquisition that will be converted into common stock upon approval of this Proposal No. 4. In addition, as described in “Executive Officers—Expected Chief Financial Officer Following the Annual Meeting” and “Proposal No. 1 Election of Directors—Director Nominees Following the Annual Meeting” Brian Stephenson, Ph.D., is expected to be appointed as our Chief Financial Officer and Drs. Hahn and Vousden and Ms. Ramasastry are expected to be appointed to our Board if the Required Company Stockholder Matters are approved. Further, in connection with the execution of the Merger Agreement, the Company and Faeth Subsidiary entered into Support Agreements with certain of our officers and directors (solely in their capacity as stockholders), representing approximately 1.5% of shares of common stock outstanding on the record date. The Support Agreements provide that, among other things, each of the parties thereto has agreed to vote or cause to be voted all of the shares of common stock beneficially owned by such stockholder in favor of Proposals Nos. 3, 4, 5 and 6 at the Annual Meeting, subject to and in accordance with the terms of the Support Agreements.

THE BOARD OF DIRECTORS RECOMMENDS

A VOTE “FOR” PROPOSAL NO. 4.

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PROPOSAL NO. 5

APPROVAL OF THE 2026 EQUITY INCENTIVE PLAN

Overview

The Company’s stockholders are also being asked to consider and vote upon the 2026 Plan Proposal to approve the Company’s 2026 Equity Incentive Plan (the “2026 Plan”). Our board of directors approved the 2026 Plan on April 10, 2026, and approved the grant of an award covering a total of 220,000 shares of our common stock, in each case subject to stockholder approval. If the Company’s stockholders approve the 2026 Plan, the 2026 Plan and such awards will immediately become effective. If the 2026 Plan is not approved by the Company’s stockholders, the 2026 Plan and such awards will not become effective, and no awards will be granted under the 2026 Plan. The 2026 Plan is described in more detail below.

The summary is qualified in its entirety by reference to the text of the 2026 Plan, a copy of which is attached as Annex C to this proxy statement. The Company’s stockholders should refer to the 2026 Plan for a more complete and detailed information about the terms and conditions of the 2026 Plan.

We Manage Our Equity Award Use Carefully

We continue to believe that equity awards are a vital part of our overall compensation program. Our compensation philosophy reflects broad-based eligibility for equity awards, and we grant equity awards to substantially all of our employees. However, we recognize that equity awards dilute existing stockholders, and, therefore, we must responsibly manage the growth of our equity compensation program. We are committed to effectively monitoring our equity compensation share reserve, including our “burn rate,” in a manner intended to maximize stockholders’ value by granting the appropriate number of equity awards necessary to attract, reward, and retain employees.

Burn Rate

The following table provides detailed information regarding the activity related to the Company’s equity incentive program for fiscal years 2025, 2024 and 2023 but does not include information regarding any equity incentive programs of Faeth.

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Overhang

The following table provides certain information regarding the Company’s equity incentive programs but does not include information on any equity incentive programs of Faeth.

2026 Equity Incentive Plan

The 2026 Plan will be the successor to and continuation of the Sensei Biotherapeutics, Inc. 2021 Equity Incentive Plan (the “2021 Plan”). Once the 2026 Plan becomes effective, no further grants will be made under the 2021 Plan.

Eligibility. Any individual who is an employee of ours or any of our affiliates, or any person who provides services to us or our affiliates, including members of our board of directors, is eligible to receive awards under the 2026 Plan at the discretion of the plan administrator. As of March 23, 2026, we had 29 employees, approximately five consultants, and four non-employee directors.

Types of Awards. The 2026 Plan provides for the grant of incentive stock options (“ISOs”) to employees, including employees of any parent or subsidiary, and for the grant of nonstatutory stock options (“NSOs”), stock appreciation rights, restricted stock awards, restricted stock unit awards, performance awards and other forms of stock awards to employees, directors, and consultants, including employees and consultants of our affiliates.

Authorized Shares. Subject to adjustment for specified changes in our capitalization, the maximum number of shares of our common stock that will be available for issuance under the 2026 Plan will be equal to (i) 2,671,981 shares of common stock, plus up to (ii) 311,164 shares of our common stock subject to outstanding stock awards granted under the 2021 Plan that, after the date the 2026 Plan becomes effective, are not issued because a stock award expires or otherwise terminates without all of the shares covered by the award having been issued; are not issued because the stock award is settled in cash; are forfeited or repurchased because of the failure to vest; or are reacquired or withheld to satisfy a tax withholding obligation or the purchase or exercise price (the shares described in clause (ii), the “Returning Shares”). Options to purchase Faeth common stock that were converted into options to purchase our common stock as part of the Merger are not counted against the foregoing equity pool established by the 2026 Plan, and none of the shares subject to such options will be added to such equity pool as Returning Shares. In addition, the number of shares of our common stock reserved for issuance under the 2026 Plan will automatically increase on January 1 of each calendar year, from January 1,

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2027 through January 1, 2036, in an amount equal to 5% of the total number of shares of all classes of our common stock outstanding plus all shares of our common stock issuable upon the exercise of any pre-funded warrants (without regard to any beneficial ownership limitations) on December 31 of the preceding year, or a lesser number of shares determined by our board of directors. The maximum number of shares of our common stock that may be issued on the exercise of ISOs under the 2026 Plan is equal to 8,949,435 shares. As of April 13, 2026, the closing price of the Company’s common stock as reported on Nasdaq was $30.15 per share.

Shares subject to stock awards granted under the 2026 Plan that expire or terminate without being exercised in full, or that are paid out in cash rather than in shares, do not reduce the number of shares available for issuance under the 2026 Plan. Additionally, shares become available for future grant under the 2026 Plan if (i) they were issued stock awards under the 2026 Plan and we repurchase them or they are forfeited because of the failure to vest, or (ii) they are reacquired by us to pay the exercise price of a stock award or to satisfy the tax withholding obligations related to a stock award.

Plan Administration. Our board of directors, or a duly authorized committee of our board of directors, will administer the 2026 Plan. Our board of directors may delegate concurrent authority to administer the 2026 Plan to our compensation committee under the terms of our compensation committee’s charter. We sometimes refer to our board of directors, or the applicable committee with the power to administer our equity incentive plans, as the administrator. The administrator may also delegate to one or more persons or bodies the authority to (i) designate employees (other than officers) to receive specified awards, and (ii) determine the number of shares subject to such awards. Such persons or bodies may not grant a stock award to themselves and neither our board of directors nor any committee may delegate authority to any person or body (who is not a member of our board of directors or such body that is not comprised solely of members of our board of directors) the authority to determine the fair market value of our common stock for purposes of the 2026 Plan.

The administrator has the authority to determine the terms of awards, including recipients, the exercise, purchase or strike price of awards, if any, the number of shares subject to each award, the fair market value of a share of common stock, the vesting schedule applicable to the awards, together with any vesting acceleration, and the form of consideration, if any, payable upon exercise or settlement of the award and the terms of the award agreements for use under the 2026 Plan.

In addition, subject to the terms of the 2026 Plan, the administrator also has the power to modify outstanding awards under the 2026 Plan, including the authority to reprice any outstanding option or stock appreciation right, cancel and re-grant any outstanding option or stock appreciation right in exchange for new stock awards, cash or other consideration, or take any other action that is treated as a repricing under generally accepted accounting principles, with the consent of any materially adversely affected participant.

Stock Options. ISOs and NSOs are granted under applicable award agreements adopted by the administrator. The administrator determines the exercise price for stock options, within the terms and conditions of the 2026 Plan, provided that the exercise price of a stock option generally cannot be less than 100% of the fair market value of our common stock on the date of grant. Options granted under the 2026 Plan vest at the rate specified in the applicable award agreement as determined by the administrator.

Tax Limitations on ISOs. The aggregate fair market value, determined at the time of grant, of our common stock with respect to ISOs that are exercisable for the first time by an optionholder during any calendar year under all of our stock plans may not exceed $100,000. Options or portions thereof that exceed such limit will generally be treated as NSOs. No ISO may be granted to any person who, at the time of the grant, owns or is deemed to own stock possessing more than 10% of our total combined voting power or that of any of our affiliates unless (i) the option exercise price is at least 110% of the fair market value of the stock subject to the option on the date of grant; and (ii) the option is not exercisable after the expiration of five years from the date of grant.

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Restricted Stock Unit Awards. Restricted stock units are granted under the applicable award agreements adopted by the administrator. Restricted stock units may be granted in consideration for any form of legal consideration that may be acceptable to our board of directors and permissible under applicable law. A restricted stock unit may be settled by cash, delivery of stock, a combination of cash and stock as deemed appropriate by the administrator, or in any other form of consideration set forth in the applicable award agreement. Additionally, dividend equivalents may be credited in respect of shares covered by a restricted stock unit. Except as otherwise provided in the applicable award agreement, restricted stock units that have not vested will be forfeited once the participant’s continuous service ends for any reason.

Restricted Stock Awards. Restricted stock awards are granted under applicable award agreements adopted by the administrator. A restricted stock award may be awarded in consideration for cash, check, bank draft or money order, past services to us, or any other form of legal consideration (including future services) that may be acceptable to our board of directors and permissible under applicable law. The administrator determines the terms and conditions of restricted stock awards, including vesting and forfeiture terms. If a participant’s service relationship with us ends for any reason, we may receive any or all of the shares of our common stock held by the participant that have not vested as of the date the participant terminates service with us through a forfeiture condition or a repurchase right.

Stock Appreciation Rights. Stock appreciation rights are granted under applicable award agreements adopted by the administrator. The administrator determines the purchase price or strike price for a stock appreciation right, which generally cannot be less than 100% of the fair market value of our common stock on the date of grant. A stock appreciation right granted under the 2026 Plan vests at the rate specified in the applicable award agreement as determined by the administrator.

Performance Awards. The 2026 Plan permits the grant of performance-based stock and cash awards. The administrator may structure awards so that the shares of our stock, cash, or other property will be issued or paid only following the achievement of certain pre-established performance goals during a designated performance period. The performance criteria that will be used to establish such performance goals may be based on any one of, or combination of, the following as determined by the administrator: earnings (including earnings per share and net earnings); earnings before interest, taxes and depreciation; earnings before interest, taxes, depreciation and amortization; total stockholder return; relative stockholder return; return on equity or average stockholder’s equity; return on assets, investment, or capital employed; share price; margin (including gross margin); income (before or after taxes); operating income; operating income after taxes; pre-tax profit; operating cash flow; sales, annual recurring revenue, or revenue targets; increases in revenue or product revenue; expenses and cost reduction goals; improvement in or attainment of working capital levels; economic value added (or an equivalent metric); market share; cash flow; cash flow per share; share price performance; debt reduction; customer satisfaction; stockholder’s equity; capital expenditures; debt levels; operating profit or net operating profit; growth of net income or operating income; billings; financing; regulatory milestones; stockholder liquidity; corporate governance and compliance; intellectual property; personnel matters; progress of internal research; progress of partnered programs; partner satisfaction; budget management; partner or collaborator achievements; internal controls, including those related to the Sarbanes-Oxley Act of 2002; investor relations, analysts and communication; implementation or completion of projects or processes; employee retention; strategic partnerships or transactions (including in-licensing and out-licensing of intellectual property); establishing relationships with respect to the marketing, distribution and sale of the Company’s products; supply chain achievements; co-development, co-marketing, profit sharing, joint venture or other similar arrangements; individual performance goals; corporate development and planning goals; and other measures of performance selected by the administrator.

The performance goals may be based on a company-wide basis, with respect to one or more business units, divisions, affiliates, or business segments, and in either absolute terms or relative to the performance of one or more comparable companies or the performance of one or more relevant indices. Unless specified otherwise (i) in the award agreement at the time the award is granted or (ii) in such other document setting forth the

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performance goals at the time the goals are established, we will appropriately make adjustments in the method of calculating the attainment of performance goals as follows: (1) to exclude restructuring and/or other nonrecurring charges; (2) to exclude exchange rate effects; (3) to exclude the effects of changes to generally accepted accounting principles; (4) to exclude the effects of any statutory adjustments to corporate tax rates; (5) to exclude the effects of items that are “unusual” in nature or occur “infrequently” as determined under generally accepted accounting principles; (6) to exclude the dilutive effects of acquisitions or joint ventures; (7) to assume that any business divested by us achieved performance objectives at targeted levels during the balance of a performance period following such divestiture; (8) to exclude the effect of any change in the outstanding shares of our common stock by reason of any stock dividend or split, stock repurchase, reorganization, recapitalization, merger, consolidation, spin-off, combination or exchange of shares or other similar corporate change, or any distributions to common stockholders other than regular cash dividends; (9) to exclude the effects of stock based compensation and the award of bonuses under our bonus plans; (10) to exclude costs incurred in connection with potential acquisitions or divestitures that are required to be expensed under generally accepted accounting principles; and (11) to exclude the goodwill and intangible asset impairment charges that are required to be recorded under generally accepted accounting principles. The administrator retains the discretion to reduce or eliminate the compensation or economic benefit due upon attainment of the goals. The performance goals may differ from participant to participant and from award to award.

Other Stock Awards. The administrator may grant other awards based in whole or in part by reference to our common stock. The administrator will set the number of shares under the stock award and all other terms and conditions of such awards.

Non-Employee Director Compensation Limit. The aggregate value of all compensation granted or paid to any non-employee director with respect to any fiscal year, including stock awards granted and cash fees paid by us to such non-employee director, will not exceed $750,000 in total value, or in the event such non-employee director is first appointed or elected to our board of directors during such calendar year, $1,000,000 in total value (in each case, calculating the value of any such stock awards based on the grant date fair value of such stock awards for financial reporting purposes). Compensation will count towards this limit for the fiscal year in which it was granted or earned, and not later when distributed, in the event it is deferred.

Changes to Capital Structure. In the event there is a specified type of change in our capital structure, such as a stock split, reverse stock split, or recapitalization, appropriate adjustments will be made to (i) the class and maximum number of shares reserved for issuance under the 2026 Plan, (ii) the class and maximum number of shares by which the share reserve may increase automatically each year, (iii) the class and maximum number of shares that may be issued on the exercise of ISOs, and (iv) the class and number of shares and exercise price, strike price, or purchase price, if applicable, of all outstanding stock awards.

Corporate Transactions. The following applies to stock awards under the 2026 Plan in the event of a corporate transaction, unless otherwise provided in a participant’s stock award agreement or other written agreement with us or one of our affiliates or unless otherwise expressly provided by the administrator at the time of grant.

In the event of a corporate transaction, any stock awards outstanding under the 2026 Plan may be assumed, continued or substituted for by any surviving or acquiring corporation (or its parent company), and any reacquisition or repurchase rights held by us with respect to the stock award may be assigned to the successor (or its parent company). If the surviving or acquiring corporation (or its parent company) does not assume, continue or substitute for such stock awards, then with respect to any such stock awards that are held by participants whose continuous service has not terminated prior to the effective time of the transaction, or current participants, the vesting (and exercisability, if applicable) of such stock awards will be accelerated in full to a date prior to the effective time of the transaction (contingent upon the effectiveness of the transaction), and such stock awards will terminate if not exercised (if applicable) at or prior to the effective time of the transaction, and any reacquisition or repurchase rights held by us with respect to such stock awards will lapse (contingent upon the

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effectiveness of the transaction). With respect to performance awards with multiple vesting levels depending on performance level, unless otherwise provided by an award agreement or by the administrator, the award will accelerate at 100% of target. If the surviving or acquiring corporation (or its parent company) does not assume, continue or substitute for such stock awards, then with respect to any such stock awards that are held by persons other than current participants, such awards will terminate if not exercised (if applicable) prior to the effective time of the transaction, except that any reacquisition or repurchase rights held by us with respect to such stock awards will not terminate and may continue to be exercised notwithstanding the transaction. The administrator is not obligated to treat all stock awards or portions of stock awards in the same manner and is not obligated to take the same actions with respect to all participants.

In the event a stock award will terminate if not exercised prior to the effective time of a transaction, the administrator may provide, in its sole discretion, that the holder of such stock award may not exercise such stock award but instead will receive a payment equal in value to the excess (if any) of (i) the value of the property the participant would have received upon the exercise of the stock award over (ii) any exercise price payable by such holder in connection with such exercise.

Under the 2026 Plan, a corporate transaction is defined to include the consummation, in a single transaction or in a series of related transactions, of any one or more of the following events: (i) a sale or disposition of all or substantially all of our assets; (ii) a sale or disposition of more than 50% of our outstanding securities; (iii) a merger, consolidation or similar transaction where we do not survive the transaction; and (iv) a merger or consolidation where we do survive the transaction but the shares of our common stock outstanding before such transaction are converted or exchanged into other property by virtue of the transaction, unless otherwise provided in an award agreement or other written agreement between us and the award holder.

Change in Control. In the event of a change in control, as defined under the 2026 Plan, awards granted under the 2026 Plan will not receive automatic acceleration of vesting and exercisability, although this treatment may be provided for in an award agreement.

Under the 2026 Plan, a change in control is defined to include: (i) the acquisition by any person or company of more than 50% of the combined voting power of our then outstanding stock; (ii) a consummated merger, consolidation or similar transaction in which our stockholders immediately before the transaction do not own, directly or indirectly, more than 50% of the combined voting power of the surviving entity (or the parent of the surviving entity); (iii) a consummated sale, lease, exclusive license or other disposition of all or substantially all of our assets other than to an entity more than 50% of the combined voting power of which is owned by our stockholders; and (iv) an unapproved change in the majority of the board of directors.

Transferability. A participant may not transfer stock awards under the 2026 Plan other than by will, the laws of descent and distribution, or as otherwise provided under the 2026 Plan.

Clawback/Recovery. All awards granted under the 2026 Plan will be subject to recoupment in accordance with any clawback policy that we are required to adopt pursuant to the listing standards of any national securities exchange or association on which our securities are listed or as is otherwise required by the U.S. Dodd-Frank Wall Street Reform and Consumer Protection Act or other applicable law. In addition, our board of directors may impose such other clawback, recovery or recoupment provisions in a stock award agreement as our board of directors determines necessary or appropriate.

Plan Amendment or Termination. Our board of directors has the authority to amend, suspend, or terminate the 2026 Plan, provided that such action does not materially impair the existing rights of any participant without such participant’s written consent. Certain material amendments also require the approval of our stockholders. No ISOs may be granted after the tenth anniversary of the date our board of directors adopted the 2026 Plan. No stock awards may be granted under the 2026 Plan while it is suspended or after it is terminated.

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U.S. Federal Income Tax Consequences

The following is a summary of the principal U.S. federal income tax consequences to participants and the Company with respect to participation in the 2026 Plan. This summary is not intended to be exhaustive and does not discuss the income tax laws of any local, state or foreign jurisdiction in which a participant may reside. The information is based upon current U.S. federal income tax rules and therefore is subject to change when those rules change. Because the tax consequences to any participant may depend on his or her particular situation, each participant should consult the participant’s tax adviser regarding the federal, state, local and other tax consequences of the grant or exercise of an award or the disposition of stock acquired under the 2026 Plan. The 2026 Plan is not qualified under the provisions of Section 401(a) of the Code and is not subject to any of the provisions of the Employee Retirement Income Security Act of 1974, as amended. The Company’s ability to realize the benefit of any tax deductions described below depends on the Company’s generation of taxable income as well as the requirement of reasonableness and the satisfaction of the Company’s tax reporting obligations.

Tax Consequences to the Participants

Nonstatutory Stock Options. Generally, there is no taxation upon the grant of an NSO. Upon exercise, a participant will recognize ordinary income equal to the excess, if any, of the fair market value of the underlying stock on the date of exercise of the stock option over the exercise price. If the participant is employed by the Company or one of its affiliates, that income will be subject to withholding taxes. The participant’s tax basis in those shares will be equal to their fair market value on the date of exercise of the stock option, and the participant’s capital gain holding period for those shares will begin on the day after they are transferred to the participant.

Incentive Stock Options. The 2026 Plan provides for the grant of stock options that are intended to qualify as “incentive stock options,” as defined in Section 422 of the Code. Under the Code, a participant generally is not subject to ordinary income tax upon the grant or exercise of an ISO. If the participant holds a share received upon exercise of an ISO for more than two years from the date the stock option was granted and more than one year from the date the stock option was exercised, which is referred to as the required holding period, the difference, if any, between the amount realized on a sale or other taxable disposition of that share and the participant’s tax basis in that share will be long-term capital gain or loss. If, however, a participant disposes of a share acquired upon exercise of an ISO before the end of the required holding period, which is referred to as a disqualifying disposition, the participant generally will recognize ordinary income in the year of the disqualifying disposition equal to the excess, if any, of the fair market value of the share on the date of exercise of the stock option over the exercise price. However, if the sales proceeds are less than the fair market value of the share on the date of exercise of the stock option, the amount of ordinary income recognized by the participant will not exceed the gain, if any, realized on the sale. If the amount realized on a disqualifying disposition exceeds the fair market value of the share on the date of exercise of the stock option, that excess will be short-term or long-term capital gain, depending on whether the holding period for the share exceeds one year. For purposes of the alternative minimum tax, the amount by which the fair market value of a share of stock acquired upon exercise of an ISO exceeds the exercise price of the stock option generally will be an adjustment included in the participant’s alternative minimum taxable income for the year in which the stock option is exercised. If, however, there is a disqualifying disposition of the share in the year in which the stock option is exercised, there will be no adjustment for alternative minimum tax purposes with respect to that share. In computing alternative minimum taxable income, the tax basis of a share acquired upon exercise of an ISO is increased by the amount of the adjustment taken into account with respect to that share for alternative minimum tax purposes in the year the stock option is exercised.

Restricted Stock Awards. Generally, the recipient of a restricted stock award will recognize ordinary income at the time the stock is received equal to the excess, if any, of the fair market value of the stock received over any amount paid by the recipient in exchange for the stock. If, however, the stock is subject to restrictions

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constituting a substantial risk of forfeiture when it is received (for example, if the employee is required to work for a period of time in order to have the right to transfer or sell the stock), the recipient generally will not recognize income until the restrictions constituting a substantial risk of forfeiture lapse, at which time the recipient will recognize ordinary income equal to the excess, if any, of the fair market value of the stock on the date it becomes vested over any amount paid by the recipient in exchange for the stock. A recipient may, however, file an election with the IRS, within 30 days following the date of grant, to recognize ordinary income, as of the date of grant, equal to the excess, if any, of the fair market value of the stock on the date the award is granted over any amount paid by the recipient for the stock. The recipient’s basis for the determination of gain or loss upon the subsequent disposition of shares acquired from a restricted stock award will be the amount paid for such shares plus any ordinary income recognized either when the stock is received or when the restrictions constituting a substantial risk of forfeiture lapse.

Restricted Stock Unit Awards. Generally, the recipient of a restricted stock unit award will generally recognize ordinary income at the time the stock is delivered equal to the excess, if any, of (i) the fair market value of the stock received over any amount paid by the recipient in exchange for the stock or (ii) the amount of cash paid to the participant. The recipient’s basis for the determination of gain or loss upon the subsequent disposition of shares acquired from a restricted stock unit award will be the amount paid for such shares plus any ordinary income recognized when the stock is delivered, and the participant’s capital gain holding period for those shares will begin on the day after they are transferred to the participant.

Stock Appreciation Rights. Generally, the recipient of a stock appreciation right will recognize ordinary income equal to the fair market value of the stock or cash received upon such exercise. For any shares received upon exercise of a stock appreciation right, the participant’s tax basis in those shares will be equal to their fair market value on the date of exercise of the stock option, and the participant’s capital gain holding period for those shares will begin on the day after they are transferred to the participant.

Tax Consequences to the Company

Subject to the requirement of reasonableness, the deduction limits under Section 162(m) of the Code and the satisfaction of a tax reporting obligation, the Company will generally be entitled to a tax deduction equal to the taxable ordinary income realized by the recipient of an award under the Plan.

Section 162(m) of the Code limits the Company’s ability to deduct compensation, for U.S. federal income tax purposes, paid during any year to a “covered employee” (within the meaning of Section 162(m) of the Code) in excess of $1 million.

New Plan Benefits

As of April 13, 2026, awards covering a total of 220,000 shares of the Company’s common stock have been contingently granted under the 2026 Plan, subject to stockholder approval of the 2026 Plan under this Proposal No. 5. The following table shows information regarding the grant of such awards (regardless of whether subsequently exercised or forfeited) to the persons and groups identified below.

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Registration with the SEC

If the 2026 Plan is approved by our stockholders and becomes effective, the Company intends to file a registration statement on Form S-8 registering the shares reserved for issuance under the 2026 Plan as soon as reasonably practicable after approval of this Proposal No. 5.

THE BOARD OF DIRECTORS RECOMMENDS

A VOTE “FOR” PROPOSAL NO. 5.

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PROPOSAL NO. 6

APPROVAL OF THE 2026 ESPP

Overview

The Company’s stockholders are also being asked to consider and vote upon the 2026 ESPP Proposal to approve the Company’s 2026 Employee Stock Purchase Plan (the “2026 ESPP”). Our board of directors approved the ESPP on April 10, 2026, subject to stockholder approval. If the Company’s stockholders approve the 2026 ESPP, the ESPP will immediately become effective. If the ESPP is not approved by the Company’s stockholders, it will not become effective. The ESPP is described in more detail below.

The summary is qualified in its entirety by reference to the text of the 2026 ESPP, a copy of which is attached as Annex D to this proxy statement. The Company’s stockholders should refer to the 2026 ESPP for a more complete and detailed information about the terms and conditions of the 2026 ESPP.

2026 Employee Stock Purchase Plan

The purpose of the 2026 ESPP is to secure and retain the services of new employees, to retain the services of existing employees, and to provide incentives for such individuals to exert maximum efforts toward our success and that of our affiliates. Our 2026 ESPP will include two components. One component will be designed to allow eligible U.S. employees to purchase our common stock in a manner that may qualify for favorable tax treatment under Section 423 of the Code. The other component will permit the grant of purchase rights that do not qualify for such favorable tax treatment in order to allow deviations necessary to permit participation by eligible employees who are foreign nationals or employed outside of the U.S. while complying with applicable foreign laws.

Eligibility. Our employees and the employees of any of our designated affiliates, will be eligible to participate in the 2026 ESPP, provided they may have to satisfy one or more of the following service requirements before participating in the 2026 ESPP, as determined by the administrator: (1) customary employment with us or one of our affiliates for more than 20 hours per week and more than five months per calendar year or (2) continuous employment with us or one of our affiliates for a minimum period of time, not to exceed two years, prior to the first date of an offering. In addition, our board of directors may also exclude from participation in the 2026 ESPP or any offering, employees who are “highly compensated employees” (within the meaning of Section 423(b)(4)(D) of the Code) or a subset of such highly compensated employees. As of March 23, 2026, we had 29 employees. An employee may not be granted rights to purchase stock under the 423 Component of the 2026 ESPP (a) if such employee immediately after the grant would own stock (including stock issuable upon exercise of all such employee’s purchase rights) possessing 5% or more of the total combined voting power or value of all classes of our common stock or (b) to the extent that such rights would accrue at a rate that exceeds $25,000 worth of our common stock for each calendar year that the rights remain outstanding. Our board of directors may approve different eligibility rules for the Non-423 Component.

Share Reserve. The 2026 ESPP authorizes the issuance of shares of our common stock under purchase rights granted to our employees or to employees of any of our designated affiliates. Subject to adjustment for specified changes in our capitalization, the maximum number of shares of our common stock that may be issued under the 2026 ESPP will not exceed 267,198 (the “Initial Share Reserve”). Additionally, the number of shares of our common stock reserved for issuance under the 2026 ESPP will automatically increase on January 1 of each calendar year, beginning on January 1, 2027 (assuming the 2026 ESPP becomes effective in 2026) through January 1, 2036, by the lesser of (i) 1% of the total number of shares of all classes of our common stock outstanding plus all shares of our common stock issuable upon the exercise of any pre-funded warrants (without regard to any beneficial ownership limitations), on December 31 of the preceding calendar year, and (ii) a number of shares equal to two times the Initial Share Reserve; provided that before the date of any such increase, our board of directors may determine that such increase will be less than the amount set forth in clauses (i) and (ii). As of April 13, 2026, the closing price of the Company’s common stock as reported on Nasdaq was $30.15 per share.

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Administration. Our board of directors, or a duly authorized committee thereof, will administer our 2026 ESPP. Our board may delegate concurrent authority to administer the 2026 ESPP to our compensation committee under the terms of the compensation committee’s charter. The 2026 ESPP is implemented through a series of offerings under which eligible employees are granted purchase rights to purchase shares of our common stock on specified dates during such offerings. Under the 2026 ESPP, we may specify offerings with durations of not more than 27 months and may specify shorter purchase periods within each offering. Each offering will have one or more purchase dates on which shares of our common stock will be purchased for employees participating in the offering. An offering under the 2026 ESPP may be terminated under certain circumstances.

Payroll Deductions. Generally, all regular employees, including executive officers, employed by us or by any of our designated affiliates, will be eligible to participate in the 2026 ESPP and to contribute, normally through payroll deductions, up to a maximum percentage of their earnings (as defined in the 2026 ESPP) or up to a set dollar amount for the purchase of our common stock under the 2026 ESPP, in each case not exceeding 15% of the employee’s earnings. Unless otherwise determined by our board of directors, common stock will be purchased for the accounts of employees participating in the 2026 ESPP at a price per share that is at least the lesser of (i) 85% of the fair market value of a share of our common stock on the first date of an offering; or (ii) 85% of the fair market value of a share of our common stock on the date of purchase.

Limitations. Employees may have to satisfy one or more of the following service requirements before participating in the 2026 ESPP, as determined by our board of directors, including: (i) customary employment with us or one of our affiliates for more than 20 hours per week and more than five months per calendar year; or (ii) continuous employment with us or one of our affiliates for a minimum period of time (not to exceed two years). No employee may purchase shares under the 2026 ESPP at a rate in excess of $25,000 worth of our common stock based on the fair market value per share of our common stock at the beginning of an offering for each year such a purchase right is outstanding. Finally, no employee will be eligible for the grant of any purchase rights under the 2026 ESPP if immediately after such rights are granted, such employee has voting power over 5% or more of our outstanding capital stock measured by vote or value under Section 424(d) of the Code.

Changes to Capital Structure. In the event that there occurs a change in our capital structure through such actions as a stock split, merger, consolidation, reorganization, recapitalization, reincorporation, stock dividend, dividend in property other than cash, large nonrecurring cash dividend, liquidating dividend, combination of shares, exchange of shares, change in corporate structure, or similar transaction, the board of directors will make appropriate adjustments to: (i) the number of shares reserved under the 2026 ESPP; (ii) the maximum number of shares by which the share reserve may increase automatically each year; (iii) the number of shares and purchase price of all outstanding purchase rights; and (iv) the number of shares that are subject to purchase limits under ongoing offerings.

Corporate Transactions. In the event of certain significant corporate transactions, including the consummation, in a single transaction or in a series of related transactions, of any one or more of the following events: (i) a sale of all or substantially all of our assets; (ii) a sale or disposition of more than 50% of our outstanding securities; (iii) a merger or consolidation where we do not survive the transaction; and (iv) a merger or consolidation where we do survive the transaction but the shares of our common stock outstanding immediately before such transaction are converted or exchanged into other property by virtue of the transaction, any then-outstanding rights to purchase our stock under the 2026 ESPP may be assumed, continued or substituted for by any surviving or acquiring entity (or its parent company). If the surviving or acquiring entity (or its parent company) elects not to assume, continue, or substitute for such purchase rights, then the participants’ accumulated payroll contributions will be used to purchase shares of our common stock within ten business days before such corporate transaction, and such purchase rights will terminate immediately after such purchase.

2026 ESPP Amendment or Termination. Our board of directors has the authority to amend or terminate our 2026 ESPP, provided that except in certain circumstances such amendment or termination may not materially impair any outstanding purchase rights without the holder’s consent. We will obtain stockholder approval of any

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amendment to our 2026 ESPP as required by applicable law or listing requirements. If the 2026 ESPP is terminated, the Board, in its discretion, may elect to terminate all outstanding offerings either immediately or upon completion of the purchase of shares of common stock on the next purchase date (which may be sooner than originally scheduled, if determined by the Board in its discretion), or may elect to permit offering to expire in accordance with their terms.

U.S. Federal Income Tax Consequences

The following is a summary of the principal U.S. federal income tax consequences to participants and the Company with respect to participation in the 2026 ESPP. This summary is not intended to be exhaustive and does not discuss the income tax laws of any local, state or foreign jurisdiction in which a participant may reside. The information is based upon current U.S. federal income tax rules and therefore is subject to change when those rules change. Because the tax consequences to any participant may depend on his or her particular situation, each participant should consult the participant’s tax adviser regarding the federal, state, local, and other tax consequences of the grant or exercise of a purchase right or the sale or other disposition of the Company’s common stock acquired under the 2026 ESPP. The 2026 ESPP is not qualified under the provisions of Section 401(a) of the Code and is not subject to any of the provisions of the Employee Retirement Income Security Act of 1974, as amended.

Tax Consequences to Participants

423 Component of the ESPP. Rights granted under the 423 Component of the 2026 ESPP are intended to qualify for favorable U.S. federal income tax treatment associated with rights granted under an employee stock purchase plan which qualifies under the provisions of Section 423 of the Code.

A participant will be taxed on amounts withheld for the purchase of shares of the Company’s common stock as if such amounts were actually received. Otherwise, no income will be taxable to a participant as a result of the granting or exercise of a purchase right until a sale or other disposition of the acquired shares. The taxation upon such sale or other disposition will depend upon the holding period of the acquired shares.

If the shares are sold or otherwise disposed of more than two years after the beginning of the offering period and more than one year after the shares are transferred to the participant, then the lesser of the following will be treated as ordinary income: (i) the excess of the fair market value of the shares at the time of such sale or other disposition over the purchase price; or (ii) the excess of the fair market value of the shares as of the beginning of the offering period over the purchase price (determined as of the beginning of the offering period). Any further gain or any loss will be taxed as a long-term capital gain or loss.

If the shares are sold or otherwise disposed of before the expiration of either of the holding periods described above, then the excess of the fair market value of the shares on the purchase date over the purchase price will be treated as ordinary income at the time of such sale or other disposition. The balance of any gain will be treated as capital gain. Even if the shares are later sold or otherwise disposed of for less than their fair market value on the purchase date, the same amount of ordinary income is attributed to the participant, and a capital loss is recognized equal to the difference between the sales price and the fair market value of the shares on such purchase date. Any capital gain or loss will be short-term or long-term, depending on how long the shares have been held.

Non-423 Component. A participant will be taxed on amounts withheld for the purchase of shares of the Company’s common stock as if such amounts were actually received. Under the Non-423 Component, a participant will recognize ordinary income equal to the excess, if any, of the fair market value of the underlying stock on the date of exercise of the purchase right over the purchase price. If the participant is employed by the Company or one of its affiliates, that income will be subject to withholding taxes. The participant’s tax basis in

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those shares will be equal to their fair market value on the date of exercise of the purchase right, and the participant’s capital gain holding period for those shares will begin on the day after they are transferred to the participant.

Tax Consequences to the Company

There are no U.S. federal income tax consequences to the Company by reason of the grant or exercise of rights under the 2026 ESPP. The Company is entitled to a deduction to the extent amounts are taxed as ordinary income to a participant for shares sold or otherwise disposed of before the expiration of the holding periods described above (subject to the requirement of reasonableness, the deduction limits under Section 162(m) of the Code and the satisfaction of tax reporting obligations). Section 162(m) of the Code limits the Company’s ability to deduct compensation, for U.S. federal income tax purposes, paid during any year to a “covered employee” (within the meaning of Section 162(m) of the Code) in excess of $1 million.

New Plan Benefits

Participation in the 2026 ESPP is voluntary and each eligible employee will make his or her own decision regarding whether and to what extent to participate in the 2026 ESPP. Therefore, the Company cannot currently determine the benefits or number of shares subject to purchase rights and a new plan benefits table is thus not provided. In addition, the Company cannot determine the benefits or number of shares subject to purchase rights or that would have been received by an eligible employee in the last completed fiscal year if the 2026 ESPP had been in effect.

Registration with the SEC

If the 2026 ESPP is approved by our stockholders and becomes effective, the Company intends to file a registration statement on Form S-8 registering the shares reserved for issuance under the 2026 ESPP as soon as reasonably practicable after the approval of this Proposal No. 6.

THE BOARD OF DIRECTORS RECOMMENDS

A VOTE “FOR” PROPOSAL NO. 6.

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PROPOSAL NO. 7

APPROVAL OF ADJOURNMENT OR POSTPONEMENT OF THE ANNUAL MEETING TO A LATER DATE OR DATES, IF NECESSARY, TO SOLICIT VOTES FOR PROPOSALS NOS. 3, 4, 5 AND/OR 6 OR IF THE NASDAQ INITIAL LISTING APPLICATION HAS NOT YET BEEN APPROVED

If at the Annual Meeting the number of votes represented by shares of our common stock present or represented and voting in favor of any of Proposals Nos. 3, 4, 5 and/or 6 is insufficient to approve the applicable Proposal or if Nasdaq has not approved the Nasdaq Listing Application as of immediately prior to the Annual Meeting, our management may move to adjourn the Annual Meeting in order to enable our Board to continue to solicit additional proxies in favor of any of Proposals Nos. 3, 4, 5 and/or 6 or to postpone the Annual Meeting if the Nasdaq Listing Application required by Nasdaq Listing Rule 5110(a) has not yet been approved.

In this Proposal, we are asking our stockholders to authorize the holder of any proxy solicited to vote in favor of adjourning, postponing or continuing the Annual Meeting and any later adjournments. If our stockholders approve the adjournment, postponement or continuation proposal, we could adjourn, postpone or continue the Annual Meeting, and any adjourned session of the Annual Meeting, to use the additional time to solicit additional proxies in favor of any of Proposals Nos. 3, 4, 5 and/or 6, including the solicitation of proxies from stockholders that have previously voted against the Proposals, or to postpone the Annual Meeting if the Nasdaq Listing Application required by Nasdaq Listing Rule 5110(a) has not yet been approved. If stockholder approval for this Proposal is not obtained, then the Annual Meeting will not be adjourned.

We are required to use our reasonable best efforts to secure the approvals sought in Proposal No. 3 and Proposal No. 4 as soon as practicable following the date of the Annual Meeting if they are not approved at the Annual Meeting. We will be required to hold an annual meeting or a special meeting at least every six months to solicit and take a vote on the approvals sought in Proposal No. 3 and Proposal No. 4 until such approvals are obtained.

THE BOARD OF DIRECTORS RECOMMENDS

A VOTE “FOR” PROPOSAL NO. 7.

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EXECUTIVE OFFICERS

The following table sets forth information concerning our executive officers as of the date hereof:

EXECUTIVE OFFICERS WHO ARE NOT DIRECTORS

The following sets forth certain information as of the date hereof with respect to our executive officers who are not directors. This information for Messrs. Gerry and Parikh is set forth above “Proposal No. 1—Election of Directors.”

Josiah Craver, age 43

Josiah Craver has served as our Senior Vice President of Finance since July 2024 and Principal Financial and Accounting Officer since September 2024. Prior to joining Sensei, Mr. Craver was at KALA BIO, a publicly-traded biotechnology company, from November 2020 to July 2024, most recently serving as SVP of Finance and Corporate Controller and prior to that he held senior finance positions at Solid Biosciences, a publicly-traded biotechnology company, including as VP of Finance and Corporate Controller, from 2017 to 2020. Mr. Craver began his career at PricewaterhouseCoopers in the health industries audit practice, primarily serving life science and biotech companies. Mr. Craver holds an M.S. in Accountancy from Stonehill College and is a Certified Public Accountant.

EXPECTED CHIEF FINANCIAL OFFICER FOLLOWING THE ANNUAL MEETING

If the Required Company Stockholder Matters are approved, Brian Stephenson, Ph.D., is expected to be appointed as our Chief Financial Officer, effective immediately following the Annual Meeting.

Brian Stephenson, Ph.D., age 45

Brian Stephenson has served as our Head of Operations and Finance since March 2026. Prior to joining Sensei, Dr. Stephenson served as Chief Financial Officer of BridgeBio Pharma, Inc. from October 2018 to March 2025 and as a consultant from March 2025 to March 2026. Prior to that, Dr. Stephenson served as Partner and the Head of Life Sciences for Capital IP Investment Partners, a special situation investment fund, from 2015 to 2018, and from 2011 to 2014, Dr. Stephenson was at Leerink Partners, an investment bank, and McKinsey & Company from 2007 to 2011. He received his Ph.D. and M.S. degrees in chemical engineering from the Massachusetts Institute of Technology and his B.S. in chemical engineering from Brigham Young University. Dr. Stephenson is also a Chartered Financial Analyst charterholder.

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SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

The following table sets forth the beneficial ownership of our common stock as of March 31, 2026 for:

The number of shares beneficially owned by each entity, person, director or executive officer is determined in accordance with the rules of the SEC. These rules generally attribute beneficial ownership of securities to persons who possess sole or shared voting power or investment power with respect to those securities. Under these rules, beneficial ownership includes any shares of common stock over which the person has sole or shared voting power or investment power as well as any shares that the person has the right to acquire within 60 days after March 31, 2026 through the exercise of any stock option, warrant or other rights.

The percentage of shares beneficially owned is based on 1,340,333 shares of our common stock outstanding as of March 31, 2026. Shares of our common stock that a person has the right to acquire within 60 days of March 31, 2026 are deemed outstanding for purposes of computing the percentage ownership of the person holding such rights, but are not deemed outstanding for purposes of computing the percentage ownership of any other person, except with respect to the percentage ownership of all directors and executive officers as a group. Except as otherwise noted below, the address for each beneficial owner listed is c/o Sensei Biotherapeutics, Inc., 1405 Research Blvd, Suite 125, Rockville, Maryland 20850.

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SECTION 16(A) BENEFICIAL OWNERSHIP REPORTING COMPLIANCE

Section 16(a) of the Exchange Act requires our directors and officers and holders of more than 10% of our common stock to file with the SEC initial reports of ownership of our common stock and other equity securities on a Form 3 and reports of changes in such ownership on a Form 4 or Form 5. Directors and officers and holders of 10% of our common stock are required by SEC regulations to furnish us with copies of all Section 16(a) forms they file.

To our knowledge, based solely on a review of our records and representations made by our directors and officers and certain of our more than 10% stockholders regarding their filing obligations, we believe that during the year ended December 31, 2025, our directors, executive officers and more than 10% stockholders complied with all applicable Section 16(a) filing requirements, except for Form 4s that were filed three days late on February 26, 2025 due to administrative error for each of Edward van der Horst and John Celebi related to shares withheld to satisfy withholding tax obligations upon the vesting of RSUs.

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EXECUTIVE COMPENSATION

Our named executive officers for the fiscal year ended December 31, 2025, consisting of our principal executive officers who served during the fiscal year, our next most highly compensated executive officer who was serving as an executive officer at the end of the fiscal year and former executive officers who would have qualified as named executive officers for the fiscal year but for the fact that they were not serving as an executive officer as of the end of the fiscal year, were:

Summary Compensation Table

The following table sets forth information concerning the compensation of our named executive officers during the fiscal years ended December 31, 2025 and 2024:

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Narrative to Summary Compensation Table

We review compensation annually for all employees, including our executive officers. In setting executive base salaries and bonuses and granting equity incentive awards, we consider compensation for comparable positions in the market, the historical compensation levels of our executives, individual performance as compared to our expectations and objectives, our desire to motivate our employees to achieve short- and long-term results that are in the best interests of our stockholders, and a long-term commitment to our company. Our Compensation Committee historically has determined to set cash compensation at approximately the 50th percentile of our peer company data for comparable positions and total equity award value between the 50th and 75th percentile, though variations on this pay positioning may occur from year to year.

The Compensation Committee of our Board of Directors has historically determined our executives’ compensation. Our Compensation Committee typically reviews and discusses management’s proposed compensation with the Chief Executive Officer for all executives other than the Chief Executive Officer. Based on those discussions and its discretion, the Compensation Committee then, without members of management present, discusses and ultimately approves the compensation of our executive officers.

Annual Base Salary

Our named executive officers receive a base salary to compensate them for services rendered to us. The base salary payable to each named executive officer is intended to provide a fixed component of compensation reflecting the executive’s skill set, experience, role and responsibilities. Mr. Celebi’s annual base salary was $554,346 until his termination in November 2025, Ms. Krebs’ annual base salary was $398,745 until her termination in November 2025 and Dr. van der Horst’s annual base salary was $410,000 until his termination in November 2025. Mr. Gerry’s annual base salary was $396,550 until November 14, 2025, when his base salary increased to $425,000, and Mr. Craver’s annual base salary was $370,800 until November 14, 2025, when his base salary increased to $400,000, with each such increase pursuant to such named executive officer’s retention agreement described in “—Employment Agreements with our Named Executive Officers—Retention Agreements”.

Annual Bonus

We seek to motivate and reward our executives for achievements relative to our corporate goals and expectations and individual performance for each fiscal year. Our named executive officers are eligible to receive annual

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bonuses of up to a percentage of the applicable executive’s gross base salary based on performance metrics, as determined by our Compensation Committee. For 2025 and 2024, the target bonus for each of Mr. Celebi, Mr. Gerry, Ms. Krebs, Dr. van der Horst and Mr. Craver was 55%, 35%, 40%, 40% and 35%, respectively, of their respective base salaries. Messrs. Gerry and Craver are eligible to receive an annual target bonus equal to 40% of their respective base salaries beginning with the year ending December 31, 2026 pursuant to such named executive officer’s retention agreement described in “—Employment Agreements with our Named Executive Officers—Retention Agreements”.

The actual performance-based annual bonus paid, if any, has historically been calculated by multiplying the executive’s annual base salary at year-end, target bonus percentage and, respectively, the percentage attainment of the corporate goals established for such year, and the percentage attainment of individual goals. However, the Compensation Committee is not required to calculate bonuses in this manner and retains discretion in the amounts it awards and the factors it takes into consideration in determining bonus amounts.

Our 2025 corporate goals consisted of research and development, business development and financial objectives. In light of the Company’s strategic alternatives review process and the subsequent execution of the Acquisition Transactions, the Compensation Committee determined not to conduct a formal assessment of the 2025 corporate goals. No annual bonuses were paid to any named executive officer for the year ended December 31, 2025. In lieu of the annual bonus program for 2025, in December 2025 the Compensation Committee approved retention bonuses for Messrs. Gerry and Craver, as described in “—Employment Agreements with our Named Executive Officers—Retention Agreements” below.

Equity-Based Incentive Awards

We believe that equity awards provide our executives with a strong link to our long-term performance, create an ownership culture and align the interests of our executives and our stockholders. We believe that our equity awards are an important retention tool for our executive officers, as well as for our other employees.

We award equity awards broadly to our employees. Grants to our executives and other employees are made at the discretion of our board of directors and Compensation Committee. Our Compensation Committee grants stock options, restricted stock units, or a combination of both to our employees, including our named executive officers.

On February 14, 2025, Mr. Celebi, Mr. Gerry, Ms. Krebs, Dr. van der Horst and Mr. Craver were granted stock options to purchase 17,999 shares, 2,500 shares, 6,000 shares, 5,500 shares and 2,500 shares, respectively. One-fourth of the shares underlying the stock options vest on February 14, 2026, with the remainder vesting monthly over an additional 36 months of continuous service.

For additional information about equity grants made historically to our named executive officers, please see “—Outstanding Equity Awards as of December 31, 2025” below.

Nonqualified Deferred Compensation

Our named executive officers did not participate in, or earn any benefits under, a nonqualified deferred compensation plan sponsored by us during fiscal 2025.

Termination or Change in Control Benefits

Each of our named executive officers’ employment agreements entitles them to certain benefits upon a qualifying termination. For additional discussion, please see “Employment Agreements with our Named Executive Officers” below.

Health and Welfare; Perquisites

All of our current named executive officers are eligible to participate in our employee benefit plans, including our medical, dental, vision, disability and life insurance plans, in each case on the same basis as all of our other

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employees. We generally do not provide perquisites or personal benefits to our named executive officers, except in limited circumstances (including Mr. Celebi’s housing and vehicle allowances).

401(k) Plan

We maintain a safe harbor 401(k) plan that provides eligible U.S. employees with an opportunity to save for retirement on a tax advantaged basis. Eligible employees are able to defer eligible compensation up to certain limits under the Code, which are updated annually. We have the ability to make matching and discretionary contributions to the 401(k) plan. Currently, we make matching contributions or discretionary contributions to the 401(k) plan up to a maximum of 4% of such employee’s annual compensation. The 401(k) plan is intended to be qualified under Section 401(a) of the Code, with the related trust intended to be tax exempt under Section 501(a) of the Code. As a tax-qualified retirement plan, contributions to the 401(k) plan are deductible by us when made, and contributions and earnings on those amounts are generally not taxable to the employees until withdrawn or distributed from the 401(k) plan.

Severance Plan

On April 10, 2026, the Board, upon recommendation of the Compensation Committee and following a review of market practices conducted by the Compensation Committee’s independent compensation consultant, Alpine Rewards, adopted the Sensei Biotherapeutics, Inc. Severance and Change in Control Plan (the “Severance and CIC Plan”), effective as of the same date, under which the Company’s executive officers and certain additional key employees are eligible to receive severance payments and benefits in connection with certain qualifying terminations of their employment with the Company, subject to the conditions set forth in the Severance and CIC Plan.

Participation in the Severance and CIC Plan is limited to employees who have been designated by the administrator of the plan as eligible to participate and who have executed a participation agreement. Messrs. Gerry, Craver and Parikh have been designated as eligible to participate in the Severance and CIC Plan.

Upon an involuntary termination by the Company without Cause or a resignation by the participant for Good Reason (in each case, excluding termination due to death or disability) (a “Covered Termination”) outside of the period beginning three months prior to and ending twelve months following a Change in Control (a “Change in Control Period”), participants are entitled to cash severance equal to a specified number of months of base salary (12 months for Mr. Parikh, nine months for Mr. Gerry and six months for Mr. Craver) (such period, the “Standard Severance Period”), paid in installments over the Standard Severance Period, plus Company-paid COBRA premiums for up to the Standard Severance Period, provided that the participant is eligible for and timely makes the necessary elections for continuation coverage. No equity acceleration is provided in connection with a Covered Termination outside of the Change in Control Period.

Upon a Covered Termination occurring during the Change in Control Period, participants are instead entitled to enhanced cash severance equal to a specified number of months of base salary (18 months for Mr. Parikh and 12 months for each of Messrs. Gerry and Craver) (such period, the “CIC Severance Period”), paid in a lump sum, plus a lump-sum bonus payment equal to a specified multiple of the participant’s target annual bonus (1.5x for Mr. Parikh and 1.0x for each of Messrs. Gerry and Craver), Company-paid COBRA premiums for up to the CIC Severance Period, and full acceleration of all then-outstanding time-based equity awards.

Receipt of benefits under the Severance and CIC Plan is conditioned upon the participant’s execution of a separation agreement containing a release of claims in favor of the Company, which must become effective within 60 days following the Covered Termination. The Severance and CIC Plan includes a “best after-tax” provision under Section 280G of the Code, pursuant to which any payments that would constitute “parachute payments” will be reduced to the safe harbor amount only if such reduction would result in a greater after-tax benefit to the participant than receiving the full payment and paying the applicable excise tax. The Severance and CIC Plan supersedes any prior individual agreement between the Company and a participant to the extent such agreement provides for equity acceleration or severance benefits, provided that if a participant’s existing

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arrangement provides more favorable terms, such participant will receive the greater benefit. All payments and benefits under the Severance and CIC Plan are subject to the Company’s clawback policy. The Severance and CIC Plan is administered by the Board or Compensation Committee and may be amended or terminated at any time, subject to the requirement that a participant’s rights under an effective participation agreement may not be adversely affected without the participant’s written consent.

Employment Agreements with our Named Executive Officers

Below are descriptions of our employment agreements with our named executive officers. The agreements generally provide for at-will employment and set forth the named executive officer’s initial base salary, target bonus, eligibility for employee benefits and severance benefits upon a qualifying termination of employment. Furthermore, each of our named executive officers has executed a form of our standard proprietary information and inventions assignment agreement. The key terms of the employment agreements with our named executive officers, including potential payments upon termination or change of control, are described below.

Employment Agreements

Mr. Celebi’s employment agreement became effective upon the closing of our initial public offering. Our employment agreement with Mr. Gerry was most recently amended and restated effective July 31, 2024 in connection with his appointment as our SVP, General Counsel. Our employment agreement with Dr. van der Horst was most recently amended and restated effective December 7, 2022 in connection with his appointment as our Chief Scientific Officer. Our employment agreement with Ms. Krebs became effective November 1, 2023 in connection with her appointment as our Chief Business Officer. Our employment agreement with Mr. Craver became effective July 22, 2024 in connection with his appointment as our Senior Vice President, Finance.

The employment agreements with Mr. Celebi, Ms. Krebs and Dr. van der Horst provided that, subject to certain conditions and limitations, upon a termination without Cause or resignation for Good Reason not in connection with a Change in Control: Mr. Celebi was eligible to receive continued payment of his base salary for 12 months; and Ms. Krebs and Dr. van der Horst were each eligible to receive continued payment of their base salaries for nine months. Each such officer was also eligible to receive Company-paid COBRA premiums for the applicable severance period.

In addition, upon a termination without Cause or resignation for Good Reason within 12 months following a Change in Control, Mr. Celebi was eligible to receive a lump-sum cash severance benefit equal to 18 months of base salary and 150% of his target bonus, and Ms. Krebs and Dr. van der Horst were each eligible to receive a lump-sum cash severance benefit equal to 12 months of base salary and 100% of the officer’s target bonus, in each case together with Company-paid COBRA premiums for the applicable severance period and full acceleration of all unvested equity awards.

The severance benefits described above were conditioned upon the applicable officer’s execution and non-revocation of a separation agreement, including a release of claims, and compliance with certain restrictive covenants.

The employment agreements with Messrs. Gerry and Craver also provide for severance benefits upon a qualifying termination, including continued base salary payments and Company-paid COBRA premiums (and, in the case of a qualifying termination in connection with a Change in Control, a lump-sum payment and equity acceleration). These severance provisions have been superseded by the Severance and CIC Plan described above, which provides severance benefits that are at least as favorable as those under their respective employment agreements in all circumstances. For a description of the severance benefits currently applicable to Messrs. Gerry and Craver, see “—Severance Plan” above.

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From time to time, we may also engage in transactions in our own securities, such as in connection with our prior stock repurchase program. We have procedures in place designed to ensure our compliance with applicable laws and regulations relating to insider trading in connection with any such transactions.

Policy on Hedging and Speculative Trading

Our insider trading and window period policy prohibits directors, officers and employees from engaging in short sales, transactions in put or call options, hedging transactions, margin accounts or other inherently speculative transactions with respect to our stock at any time.

Clawback Policy

In October 2023, the Compensation Committee adopted our Incentive Compensation Recoupment Policy (the “Clawback Policy”), designed to comply with Rule 10D-1 of the Exchange Act and Nasdaq Listing Rule 5608, which provides for recoupment of incentive compensation in the event of an accounting restatement resulting from material noncompliance with financial reporting requirements under the relevant securities laws. The Clawback Policy applies to our current and former executive officers. Compensation that is granted, earned or vested based wholly or in part upon attainment of a Financial Reporting Measure (as defined in the Clawback Policy) is subject to recoupment. A copy of our Clawback Policy is filed as Exhibit 97.1 to our Annual Report on Form 10-K for our fiscal year ended December 31, 2025.

Outstanding Equity Awards as of December 31, 2025

The following table sets forth certain information about equity awards granted to our named executive officers that remained outstanding as of December 31, 2025:

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DIRECTOR COMPENSATION

The following table sets forth information regarding the compensation earned or paid to our non-employee directors during the year ended December 31, 2025. John Celebi, our former President and Chief Executive Officer, was also a member of our Board of Directors, but did not receive any additional compensation for his service as a director. Mr. Gerry, our President and General Counsel, and our Principal Executive Officer, was appointed to the Board of Directors on February 13, 2026 but will not receive any additional compensation for his service as a director. Mr. Donenberg was appointed to the Board of Directors on February 13, 2026 and will be compensated as a director in accordance with the Company’s non-employee director compensation program described below. Mr. Parikh, our Chief Operating Officer, was appointed to the Board of Directors on February 17, 2026, but will not receive any additional compensation for his service as a director. Mr. Celebi and Mr. Gerry’s compensation as executive officers is set forth above under “Executive Compensation—Summary Compensation Table.”

Non-Employee Director Compensation Policy

In April 2026, following a review of competitive market data prepared by Alpine Rewards, the Compensation Committee’s independent compensation consultant, the Compensation Committee recommended, and the Board of Directors approved, an amended non-employee director compensation policy (the “2026 Amended Policy”).

Under the 2026 Amended Policy, each non-employee director receives cash compensation as follows:

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Under the 2026 Amended Policy, each non-employee director receives equity compensation as follows:

Initial equity award. Each new non-employee director elected or appointed to our board of directors will be granted an option to purchase 25,000 shares of our common stock, vesting in 36 substantially equal monthly installments following the grant date.

Annual equity awards. On the date of each annual meeting of stockholders of our company, each non-employee director who has served as a non-employee director for at least six months prior to such stockholder meeting and who will continue to serve on our board of directors will be granted an option to purchase 12,500 shares of our common stock, vesting in monthly installments such that the option is fully vested on the earlier of the first anniversary of the grant date or the date of our next annual stockholder meeting.

All equity awards held by a non-employee director will vest in full upon a change in control.

In addition, under the 2026 Amended Policy all stock options granted to non-employee directors shall remain exercisable following the termination of a director’s service to the Company until the earliest of (x) four years following such termination of service, (y) the expiration of the option and (z) the later of (i) the number of full years of service to the Company provided by such director and (ii) three months after termination for any reason other than death or disability, 12 months after termination due to disability or 18 months due to death. Stock options shall expire immediately upon termination of a director for cause. The foregoing provisions regarding the post-termination exercise period apply to all stock options previously granted to our directors and all stock options granted in the future.

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DESCRIPTION OF CAPITAL STOCK

General

Under our certificate of incorporation, our authorized capital stock consists of 12,500,000 shares of common stock, $0.0001 par value per share, and 10,000,000 shares of preferred stock, 25,045 shares of which are designated as Series B Non-Voting Convertible Preferred Stock and 15,045 shares of which are undesignated. Our Board may establish the rights and preferences of the undesignated preferred stock from time to time.

Common Stock

Voting Rights

Holders of our common stock are entitled to one vote per share of common stock. Our common stock does not have cumulative voting rights. Accordingly, the holders of a majority of the outstanding shares of common stock entitled to vote in any election of directors can elect all of the directors standing for election, if they so choose, other than any directors that holders of any preferred stock we may issue may be entitled to elect.

Dividends

Subject to preferences that may be applicable to any then outstanding preferred stock, holders of our common stock are entitled to receive ratably those dividends, if any, as may be declared by our Board out of legally available funds.

Liquidation

In the event of our liquidation, dissolution or winding up, the holders of our common stock will be entitled to share ratably in the assets legally available for distribution to stockholders after the payment of or provision for all of our debts and other liabilities, subject to the prior rights of any preferred stock then outstanding.

Rights and Preferences

Holders of our common stock have no preemptive rights or other subscription rights and there are no redemption or sinking funds provisions applicable to our common stock. All outstanding shares of our common stock are duly authorized, validly issued, fully paid and nonassessable. The rights, preferences and privileges of holders of our common stock are subject to and may be adversely affected by the rights of the holders of shares of any series of preferred stock that we may designate and issue in the future.

Preferred Stock

Under the terms of our certificate of incorporation, our Board has the authority, without further action by our stockholders, to issue up to 10,000,000 shares of preferred stock in one or more series, to establish from time to time the number of shares to be included in each such series, to fix the dividend, voting and other rights, preferences and privileges of the shares of each wholly unissued series and any qualifications, limitations or restrictions thereon, and to increase or decrease the number of shares of any such series, but not below the number of shares of such series then outstanding.

Our Board may authorize the issuance of preferred stock with voting or conversion rights that could adversely affect the voting power or other rights of the holders of the common stock. The issuance of preferred stock, while providing flexibility in connection with possible acquisitions and other corporate purposes, could, among other things, have the effect of delaying, deferring or preventing a change in our control and may adversely affect the market price of the common stock and the voting and other rights of the holders of common stock. We have no current plans to issue any shares of preferred stock.

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Series B Non-Voting Convertible Preferred Stock

On February 17, 2026, our Board designated 25,045 shares of preferred stock as Series B Non-Voting Convertible Preferred Stock. As of April 13, 2026, we had 24,937.493 shares of preferred stock outstanding, all of which are Series B Non-Voting Convertible Preferred Stock. Each share of Series B Non-Voting Convertible Preferred Stock is convertible into 1,000 shares of common stock, subject to certain limitations, as described above. The rights of the Series B Non-Voting Convertible Preferred Stock are set forth in the Certificate of Designation, attached as Exhibit 3.1 to our Current Report on Form 8-K filed with the SEC on February 18, 2026 (the “Certificate of Designation”). Please see “Description of Series B Preferred Stock” under Proposal No. 3 for a complete description of the Certificate of Designation and the rights of the Series B Non-Voting Convertible Preferred Stock.

Preferred Stock Purchase Rights

On March 7, 2023, a special committee of the Board adopted a stockholder rights plan and declared a dividend of one right (a “Right”) for each outstanding share of common stock of the Company. Each Right entitled the registered holder thereof under certain circumstances to purchase from the Company one ten-thousandth of a share of Series A Junior Participating Cumulative Preferred Stock. The terms of the Rights were set forth in a Stockholder Rights Agreement, dated as of March 7, 2023, between the Company and American Stock Transfer & Trust Company, LLC, as rights agent (as amended, the “Rights Agreement”).

The Rights expired pursuant to the terms of the Rights Agreement on March 7, 2025. Accordingly, on March 26, 2025, the Company filed with the Secretary of State of the State of Delaware a Certificate of Elimination eliminating from its Amended and Restated Certificate of Incorporation, as amended, the designation of certain shares of its preferred stock as Series A Junior Participating Cumulative Preferred Stock, which had been designated for potential use in connection with the Rights Agreement. As a result, all shares of preferred stock previously designated as Series A Junior Participating Cumulative Preferred Stock were eliminated and returned to the status of authorized but unissued shares of preferred stock, without designation.

Anti-Takeover Effects of Delaware Law and Our Certificate of Incorporation and Bylaws

Some provisions of Delaware law, our certificate of incorporation and our bylaws contain provisions that could make the following transactions more difficult: an acquisition of us by means of a tender offer; an acquisition of us by means of a proxy contest or otherwise; or the removal of our incumbent officers and directors. It is possible that these provisions could make it more difficult to accomplish or could deter transactions that stockholders may otherwise consider to be in their best interest or in our best interests, including transactions which provide for payment of a premium over the market price for our shares.

These provisions, summarized below, are intended to discourage coercive takeover practices and inadequate takeover bids. These provisions are also designed to encourage persons seeking to acquire control of us to first negotiate with our Board. We believe that the benefits of the increased protection of our potential ability to negotiate with the proponent of an unfriendly or unsolicited proposal to acquire or restructure us outweigh the disadvantages of discouraging these proposals because negotiation of these proposals could result in an improvement of their terms.

Stockholder Meetings

Our bylaws provide that a special meeting of stockholders may be called only by our chairman of the Board, chief executive officer or president, or by a resolution adopted by a majority of our Board.

Requirements for Advance Notification of Stockholder Nominations and Proposals

Our bylaws establish advance notice procedures with respect to stockholder proposals to be brought before a stockholder meeting and the nomination of candidates for election as directors, other than nominations made by or at the direction of the Board or a committee of the Board.

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Elimination of Stockholder Action by Written Consent

Our certificate of incorporation and bylaws eliminate the right of stockholders to act by written consent without a meeting.

Staggered Board

Our Board is divided into three classes. The directors in each class serve for a three-year term, one class being elected each year by our stockholders. This system of electing and removing directors may tend to discourage a third-party from making a tender offer or otherwise attempting to obtain control of us, because it generally makes it more difficult for stockholders to replace a majority of the directors.

Removal of Directors

Our certificate of incorporation provides that no member of our Board may be removed from office by our stockholders except for cause and, in addition to any other vote required by law, upon the approval of not less than two thirds of the total voting power of all of our outstanding voting stock then entitled to vote in the election of directors.

Stockholders Not Entitled to Cumulative Voting

Our certificate of incorporation does not permit stockholders to cumulate their votes in the election of directors. Accordingly, the holders of a majority of the outstanding shares of our common stock entitled to vote in any election of directors can elect all of the directors standing for election, if they choose, other than any directors that holders of our convertible preferred stock may be entitled to elect.

Delaware Anti-Takeover Statute

We are subject to Section 203 of the DGCL, which prohibits persons deemed to be “interested stockholders” from engaging in a “business combination” with a publicly held Delaware corporation for three years following the date these persons become interested stockholders unless the business combination is, or the transaction in which the person became an interested stockholder was, approved in a prescribed manner or another prescribed exception applies. Generally, an “interested stockholder” is a person who, together with affiliates and associates, owns, or within three years prior to the determination of interested stockholder status did own, 15% or more of a corporation’s voting stock. Generally, a “business combination” includes a merger, asset or stock sale, or other transaction resulting in a financial benefit to the interested stockholder. The existence of this provision may have an anti-takeover effect with respect to transactions not approved in advance by the Board.

Choice of Forum

Our certificate of incorporation provides that the Court of Chancery of the State of Delaware (or, if and only if the Court of Chancery of the State of Delaware lacks subject matter jurisdiction, any state court located within the State of Delaware or, if and only if all such state courts lack subject matter jurisdiction, the federal district court for the District of Delaware) and any appellate court therefrom is the sole and exclusive forum for the following claims or causes of action under the Delaware statutory or common law: (i) any derivative claim or cause of action brought on our behalf; (ii) any claim or cause of action for a breach of fiduciary duty owed by any of our current or former directors, officers, or other employees to us or our stockholders; (iii) any claim or cause of action against us or any of our current or former directors, officers or other employees arising out of or pursuant to any provision of the DGCL, our certificate of incorporation, or our bylaws (as each may be amended from time to time); (iv) any claim or cause of action seeking to interpret, apply, enforce or determine the validity of our certificate of incorporation or our bylaws (as each may be amended from time to time, including any right, obligation, or remedy thereunder); (v) any claim or cause of action as to which the DGCL confers jurisdiction to

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the Court of Chancery of the State of Delaware; and (vi) any claim or cause of action against us or any of our current or former directors, officers, or other employees governed by the internal-affairs doctrine, in all cases to the fullest extent permitted by law and subject to the court’s having personal jurisdiction over the indispensable parties named as defendants. This choice of forum provision would not apply to claims or causes of action brought to enforce a duty or liability created by the Securities Act, the Exchange Act or any other claim for which the federal courts have exclusive jurisdiction, or the Securities Act. Our certificate of incorporation provides that the federal district courts of the United States of America will be the exclusive forum for resolving any complaint asserting a cause of action arising under the Securities Act. Additionally, our certificate of incorporation provides that any person or entity holding, owning or otherwise acquiring any interest in any of our securities shall be deemed to have notice of and consented to these provisions.

Amendment of Certificate of Incorporation Provisions

The amendment of any of the above provisions, except for the provision making it possible for our Board to issue convertible preferred stock, would require approval by holders of at least two thirds of the total voting power of all of our outstanding voting stock.

The provisions of Delaware law, our certificate of incorporation and our bylaws could have the effect of discouraging others from attempting hostile takeovers and, as a consequence, they may also inhibit temporary fluctuations in the market price of our common stock that often result from actual or rumored hostile takeover attempts. These provisions may also have the effect of preventing changes in the composition of our board of directors and management. It is possible that these provisions could make it more difficult to accomplish transactions that stockholders may otherwise deem to be in their best interests.

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is Equiniti Trust Company, LLC. The transfer agent’s address is 28 Liberty Street, Floor 53, New York, NY 10005.

Exchange Listing

Our common stock is listed on the Nasdaq Capital Market under the symbol “SNSE”.

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SECURITIES AUTHORIZED FOR ISSUANCE UNDER EQUITY COMPENSATION PLANS

The following table shows information regarding our equity compensation plans in effect as of December 31, 2025.

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TRANSACTIONS WITH RELATED PERSONS

Related-Person Transactions Policy and Procedures

We have adopted a related person transaction policy that sets forth our procedures for the identification, review, consideration and approval or ratification of related person transactions. For purposes of our policy only, a related person transaction is a transaction, arrangement or relationship, or any series of similar transactions, arrangements or relationships, in which we and any related person are, were or will be participants in which the amount involved exceeds $120,000. Transactions involving compensation for services provided to us as an employee or director are not covered by this policy. A related person is any executive officer, director or beneficial owner of more than 5% of any class of our voting securities, including any of their immediate family members and any entity owned or controlled by such persons.

Under the policy, if a transaction has been identified as a related person transaction, including any transaction that was not a related person transaction when originally consummated or any transaction that was not initially identified as a related person transaction prior to consummation, our management must present information regarding the related person transaction to our Audit Committee, or, if Audit Committee approval would be inappropriate, to another independent body of our Board of Directors, for review, consideration and approval or ratification. The presentation must include a description of, among other things, the material facts, the interests, direct and indirect, of the related persons, the benefits to us of the transaction and whether the transaction is on terms that are comparable to the terms available to or from, as the case may be, an unrelated third party or to or from employees generally. Under the policy, we will collect information that we deem reasonably necessary from each director, executive officer and, to the extent feasible, significant stockholder to enable us to identify any existing or potential related-person transactions and to effectuate the terms of the policy. In addition, under our Code of Conduct, our employees and directors have an affirmative responsibility to disclose any transaction or relationship that reasonably could be expected to give rise to a conflict of interest. In considering related person transactions, our Audit Committee, or other independent body of our Board of Directors, will take into account the relevant available facts and circumstances including, but not limited to:

The policy requires that, in determining whether to approve, ratify or reject a related person transaction, our Audit Committee, or other independent body of our Board of Directors, must consider, in light of known circumstances, whether the transaction is in, or is not inconsistent with, our best interests and those of our stockholders, as our Audit Committee, or other independent body of our Board of Directors, determines in the good faith exercise of its discretion.

Certain Related Party Transactions

Except as described below, there have been no transactions since January 1, 2024 to which we have been a participant in which the amount involved exceeded or will exceed $120,000 or, during such time as we qualify as a “smaller reporting company,” the lesser of (1) $120,000 or (2) 1% of the average of our total assets for the last two completed years, and in which any of our then directors, executive officers or holders of more than 5% of our common stock at the time of such transaction, or any members of their immediate family, had or will have a direct or indirect material interest, other than compensation arrangements which are described in “Executive Compensation” and “Director Compensation.”

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Investors’ Rights Agreement

We are party to an investors’ rights agreement (the “IRA”) with certain holders of our convertible preferred stock, including our 5% stockholders and their affiliates. The IRA provides these stockholders with certain registration rights, including the right to demand that we file a registration statement or request that their shares be covered by a registration statement that we are otherwise filing, and also the right to obligate us to an agreement to provide for additional rights to demand that we file a registration statement or request that their shares be covered by a registration statement that we have filed and maintain as effective.

Indemnification Agreements

Our amended and restated certificate of incorporation contains provisions limiting the liability of directors, and our amended and restated bylaws provides that we will indemnify each of our directors and officers to the fullest extent permitted under Delaware law. Our amended and restated certificate of incorporation and amended and restated bylaws also provide our board of directors with discretion to indemnify our employees and other agents when determined appropriate by the board. In addition, we have entered into an indemnification agreement with each of our directors and executive officers, which requires us to indemnify them.

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HOUSEHOLDING OF PROXY MATERIALS

The SEC has adopted rules that permit companies and intermediaries (for example, brokers) to satisfy the delivery requirements for Annual Meeting materials with respect to two or more stockholders sharing the same address by delivering a single set of Annual Meeting materials addressed to those stockholders. This process, which is commonly referred to as “householding,” potentially means extra convenience for stockholders and cost savings for companies.

For this year’s Annual Meeting, a number of brokers with account holders who are our stockholders will be “householding” our proxy materials. A single set of Annual Meeting materials will be delivered to multiple stockholders sharing an address unless contrary instructions have been received from the affected stockholders. Once you have received notice from your broker that they will be “householding” communications to your address, “householding” will continue until you are notified otherwise or until you revoke your consent. If, at any time, you no longer wish to participate in “householding” and would prefer to receive a separate set of Annual Meeting materials, please notify your broker or us. Direct your written request to Sensei Biotherapeutics, Inc., Attn: Secretary, 1405 Research Blvd, Suite 125, Rockville, Maryland 20850. Stockholders who currently receive multiple copies of the Annual Meeting materials at their addresses and would like to request “householding” of their communications should contact their brokers.

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OTHER MATTERS

The Board of Directors knows of no other matters that will be presented for consideration at the Annual Meeting. If any other matters are properly brought before the meeting, it is the intention of the persons named in the accompanying proxy to vote on such matters in accordance with their best judgment.

By Order of the Board of Directors

Christopher W. Gerry

President, General Counsel and Secretary

Dated: April  , 2026

A copy of our Annual Report on Form 10-K for the fiscal year ended December 31, 2025 is available without charge upon written request to: Corporate Secretary, Sensei Biotherapeutics, Inc., 1405 Research Blvd, Suite 125, Rockville, Maryland 20850.

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ANNEX A

UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS

A-1

SENSEI BIOTHERAPEUTICS, INC.

UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL INFORMATION

On February 17, 2026, Sensei Biotherapeutics, Inc. (the “Company”) acquired Faeth Holdings Therapeutics, Inc. (“Faeth HoldCo”) and its wholly owned subsidiary Faeth Therapeutics, LLC (“Faeth Subsidiary” and, together with Faeth HoldCo, “Faeth Therapeutics” or “Faeth”) pursuant to an Agreement and Plan of Merger (the “Merger Agreement”), dated as of February 17, 2026, by and among the Company, its merger subsidiaries, Faeth HoldCo and Faeth Subsidiary (such transaction, the “Acquisition”).

Under the terms of the Merger Agreement, the Company issued to the stockholders of Faeth an aggregate of 10,497.0980 shares of Series B Non-Voting Convertible Preferred Stock, par value $0.0001 per share (the “Series B Preferred Stock”), representing 10,497,098 shares of common stock of the Company, par value $0.0001 per share (“Common Stock”), on an as-converted-to-common basis and without giving effect to any beneficial ownership limitations. The outstanding warrant to purchase shares of Faeth Subsidiary capital stock was converted into a warrant to purchase an aggregate of 2.1020 shares of Series B Preferred Stock, representing a warrant to purchase 2,102 shares of Common Stock on an as-converted-to-common basis and without giving effect to any beneficial ownership limitations. In addition, all outstanding options to purchase Faeth Subsidiary common stock were assumed by the Company and were converted into options to purchase an aggregate of 252,210 shares of Common Stock (the “Assumed Options”). In connection with the Acquisition, stock options to purchase 6,338,670 shares of Faeth common stock, held by certain Faeth employees, were immediately exercised by the Faeth employees, of which 5,021,724 options had their vesting accelerated. Faeth HoldCo paid $14.8 million to cover tax liabilities created by such exercise of the options.

Concurrently with the acquisition of Faeth Therapeutics, on February 17, 2026, the Company entered into a Securities Purchase Agreement (the “Purchase Agreement”) with new and returning investors to raise $200.0 million of gross proceeds in which investors were issued an aggregate of 14,440.395 shares of Series B Preferred Stock, or 14,440,395 on an as-converted-to-common basis and without giving effect to any beneficial ownership limitations, (the “PIPE Securities”) at a price of $13,850 per share, or $13.85 per share on an as-converted-to-common basis, (collectively, the “Financing”). The Financing closed on February 20, 2026.

Subject to the receipt of stockholder approval of the Parent Stockholder Matters (as defined in the Merger Agreement), each share of Series B Preferred Stock will automatically convert into 1,000 shares of Common Stock, subject to certain beneficial ownership limitations established by each holder. As a result of the transactions, equityholders of the Company immediately prior to the acquisition owned approximately 4.9% of the Common Stock, equityholders of Faeth Therapeutics immediately prior to the acquisition owned approximately 40.6% of the Common Stock and investors in the Financing owned approximately 54.5% of the Common Stock, in each case, calculated on a fully-diluted, as-converted-to-common basis (and without giving effect to any beneficial ownership limitations) using the treasury stock method and based on the implied equity values of the Company and Faeth Therapeutics.

The unaudited pro forma condensed combined financial information is provided for illustrative purposes only, does not necessarily reflect what the actual consolidated results of operations and financial position would have been had the acquisition occurred on the dates assumed and may not be useful in predicting the future consolidated results of operations or financial position. The unaudited pro forma condensed combined financial information does not give effect to the potential impact of current financial conditions, regulatory matters, operating efficiencies or other savings or expenses that may result from the Acquisition.

The unaudited pro forma condensed combined financial information is based on the assumptions and adjustments that are described in the accompanying notes. Accordingly, the pro forma adjustments are preliminary, subject to further revision as additional information becomes available and additional analyses are performed and have

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been made solely for the purpose of providing unaudited pro forma condensed combined financial information. Differences between the preliminary accounting and estimates reflected in the unaudited pro forma condensed combined financial information and the final accounting and estimates may occur and these differences could have a material impact on the accompanying unaudited pro forma condensed combined financial information and the combined Company’s future results of operations and financial position.

Accounting rules require evaluation of certain assumptions, estimates, or determination of financial statement classifications. During preparation of the unaudited pro forma condensed combined financial information, management has performed a preliminary analysis and is not aware of any material differences, and accordingly, this unaudited pro forma condensed combined financial information assumes no material differences in accounting policies of the two companies. Following the Acquisition, management will conduct a final review of the Company’s accounting policies in order to determine if differences in accounting policies require adjustment or reclassification of Faeth’s results of operations or reclassification of assets or liabilities to conform to the Company’s accounting policies and classifications. As a result of this review, management may identify differences that, when conformed, could have a material impact on these unaudited pro forma condensed combined financial statements.

The following unaudited pro forma condensed combined financial information has been prepared in accordance with Article 11 of Regulation S-X under the Securities Act of 1933, as amended (the “Securities Act”) and presents the combined historical consolidated financial position and consolidated results of operations of the Company and the historical combined financial position and results of operations of Faeth, adjusted to give effect to (i) the Acquisition and the Financing and (ii) the pro forma effects of certain assumptions and adjustments described in “Notes to the Unaudited Pro Forma Condensed Combined Financial Information” below.

The following unaudited pro forma combined financial information is presented to illustrate the estimated effects of the Acquisition and Financing, based on the historical financial statements and accounting records of the Company and Faeth after giving effect to the Acquisition and Financing and the related pro forma adjustments as described in the notes included below.

The unaudited pro forma combined statements of operations for the year ended December 31, 2025 combine the historical statements of operations of the Company and Faeth, giving effect to the Acquisition and Financing as if they had occurred on January 1, 2025. The unaudited pro forma condensed combined balance sheet data assumes that the Acquisition and Financing took place on December 31, 2025, and combines the historical balance sheets of the Company and Faeth as of such date.

The unaudited pro forma condensed combined financial information, including the notes thereto, should be read in conjunction with the separate historical financial statements of the Company and Faeth, and the Company’s management’s discussion and analysis of financial condition and results of operations included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2025, filed with the Securities and Exchange Commission (“SEC”) on March 30, 2026, and the Company’s Current Report on Form 8-K/A, filed with the SEC on April 14, 2026.

The following unaudited pro forma condensed combined financial information and related notes are based on and should be read in conjunction with the following:

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UNAUDITED PRO FORMA CONDENSED COMBINED BALANCE SHEET

AS OF DECEMBER 31, 2025

(in thousands)

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UNAUDITED PRO FORMA CONDENSED COMBINED STATEMENT OF OPERATIONS

FOR THE YEAR ENDED DECEMBER 31, 2025

(in thousands, except share and per share amounts)