Amendment: SEC Form SC 13D/A filed by Tectonic Therapeutic Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 2)*

Tectonic Therapeutic, Inc.

(Name of Issuer)

Common Stock, $0.0001 par value per share

(Title of Class of Securities)

878972108

(CUSIP Number)

Michael K. Bradshaw, Jr.

Nelson Mullins Riley & Scarborough LLP

101 Constitution Avenue NW, Suite 900

Washington, DC 20001

Tel: (202) 689-2800

Fax: (202) 689-2860

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

October 22, 2024

(Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box. ☐

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

This Amendment No. 2 to the statement on Schedule 13D (this “Statement”) with respect to the shares of common stock, par value $0.0001 per share (the “Shares”), of Tectonic Therapeutic, Inc., a Delaware corporation (the “Issuer”), originally filed by Timothy A. Springer (“Dr. Springer”) and TAS Partners LLC (“TAS”) on June 26, 2024, and amended by Amendment No. 1 to the statement on Schedule 13D to add Chafen Lu (“Dr. Lu” and, collectively with Dr. Springer and TAS, the “Reporting Persons”) as a reporting person on September 26, 2024 (such statement and amendments, as further amended herein, the “Schedule 13D”), amends the Schedule 13D as set forth below.

All capitalized terms contained herein but not otherwise defined shall have the meanings ascribed to such terms in the Schedule 13D. Except as specifically amended by this Amendment No. 2, items in the Schedule 13D are unchanged.

Item 3 of the Schedule 13D is hereby amended to be supplemented by the following:

On October 22, 2024, Dr. Springer entered into a Stock Purchase Agreement with Atlas Venture Fund X, L.P. (“Atlas”), pursuant to which Dr. Springer purchased 300,000 Shares from Atlas at a purchase price of $33.59 per share, or $10,077,000 in the aggregate, payable in cash. Dr. Springer represented that he was an “accredited investor,” as defined in Regulation D, and was acquiring such Shares for investment only and not with a view towards, or for resale in connection with, the public sale or distribution thereof. The closing occurred on October 24, 2024.

The foregoing summary of the Stock Purchase Agreement does not purport to be complete and is qualified in its entirety by reference to the full text of the Stock Purchase Agreement, a copy of which is filed as Exhibit 99.6 to this Schedule 13D.

The information set forth under Item 3 and the cover pages of this Statement is incorporated herein by reference into this Item 5.

(a) The percentages of beneficial ownership reported in this Item 5, and on each Reporting Person’s cover page to this Schedule 13D, are based on a total of 14,734,479 Shares issued and outstanding as of August 9, 2024, as reported on the Issuer’s Quarterly Report on Form 10-Q, dated August 14, 2024. The number of Shares beneficially owned by each Reporting Person has not changed since the date of event that requires filing of this Statement.

The Reporting Persons, in the aggregate, beneficially own 4,593,121 Shares, representing approximately 31.2% of such class of securities.

Dr. Springer is the beneficial owner of a total of 4,593,121 Shares, representing approximately 31.2% of the outstanding Shares and consisting of (i) 4,096,764 Shares held directly, (ii) 310,223 Shares held by TAS and (iii) 186,134 Shares held by Dr. Lu.

TAS is the beneficial owner of a total of 310,223 Shares, representing approximately 2.1% of the outstanding Shares. TAS holds all such Shares directly. Dr. Springer is the sole managing member of TAS.

Dr. Lu is the beneficial owner of a total of 186,134 Shares, representing approximately 1.3% of the outstanding Shares. Dr. Lu holds all such Shares directly. Dr. Lu is the spouse of Dr. Springer.

(b) Dr. Springer exercises sole voting and dispositive power over the Shares held by him directly and the Shares held by TAS. Dr. Springer disclaims beneficial ownership of the Shares held by TAS, except to the extent of his pecuniary interest therein. Dr. Lu exercises sole voting and dispositive power over the Shares held by her directly.

(c) The Reporting Persons have not engaged in any transactions with respect to the Shares during the 60 days before the date of this filing, except as described in Item 3 above.

(d) No person other than the Reporting Persons is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Shares.

(e) Not applicable.

[signature page follows]

SIGNATURES

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Date: October 24, 2024