SEC Form SCHEDULE 13D filed by ACELYRIN INC.

The principal business address for each of the Reporting Persons is 150 East 58th St, 14th Fl, New York, NY 10155.

International holds the shares of Common Stock of ACELYRIN, Inc. (the "Company") that are the subject of this statement. The principal business of International is to invest in securities. The principal business of Partners is to serve as an investment manager, including as the investment manager of International. The principal business of GP is to serve as the general partner of International. The principal business of Management is to serve as the general partner of Partners. The principal business of Caraway is owning GP. Mr. Samaha's principal occupation is investing, and directing the investment of assets, including by serving as the non-member manager of GP and as the managing member of Management. As a result of the foregoing relationships, (i) each of Partners and GP may be deemed to beneficially own the Shares held by International, (ii) Management may be deemed to beneficially own the Shares held by Partners, (iii) Caraway may be deemed to beneficially own the Shares held by GP, and (iv) Mr. Samaha may be deemed to beneficially own the Shares held by each of Management, GP and Caraway.

None

None

International is a Cayman Islands exempted limited partnership. Partners is a Delaware limited partnership. Each of Management, GP and Caraway are Delaware limited liability companies. Mr. Samaha is a citizen of the United States of America.

All of the Common Stock to which this statement relates were purchased on behalf of the Reporting Persons using the investment capital of the respective Reporting Person. The aggregate amount of funds used for the purchase of the securities held by the Reporting Persons was approximately $12,767,883, including commissions.

The Reporting Persons purchased the shares of Common Stock for investment purposes. The Reporting Persons believe their investment in the Company may appreciate in value in the event the Company does not consummate its proposed merger with Alumis Inc. (the "Proposed Merger"). The Reporting Persons believe the Proposed Merger is financially unsound and will likely deliver less value to shareholders than potential alternatives. In addition, the Reporting Persons believe that the Company's stockholder rights plan (the "Rights Plan"), is not in the best interests of the Company's shareholders and, based on disclosures contained in the Company's proxy statement filed on April 23, 2025, may have been adopted due to the influence of Alumis Inc.'s Chief Executive Officer over the Company. Consequently, the Reporting Persons intend to vote against the Proposed Merger and may seek to have the Rights Plan rescinded. The Reporting Persons may have conversations, meetings and other communications with the management of the Company, shareholders and other persons, in each case to discuss the Proposed Merger, the Rights Plan, the Company's business, operations, strategy, governance and related matters. Except as set forth herein or such as would occur upon completion of any of the actions discussed herein, the Reporting Persons have no present plan or proposal that would relate to or result in any of the matters set forth in subparagraphs (a)-(j) of Item 4 of Schedule 13D. The Reporting Persons intend to review their investment in the Company on a continuing basis. Depending on various factors including, without limitation, the Company's financial position and strategic direction, actions taken by the Company's board, price levels of the Common Stock, other investment opportunities available to the Reporting Persons, conditions in the securities market and general economic and industry conditions, the Reporting Persons may in the future take such actions with respect to their investment in the Company as they deem appropriate including, without limitation, purchasing additional shares of Common Stock and/or other securities of the Company (collectively, "Securities"), disposing of any or all of their Securities, in the open market or otherwise, at any time and from time to time, and engaging in any hedging or similar transactions with respect to the Securities. The Reporting Persons reserve the right to change their intention with respect to any and all matters referred to in this Item 4 of this Schedule 13D.

The aggregate number is 5,089,260 shares of Common Stock. This represents approximately 5.1% of the outstanding Common Stock, assuming 100,709,853 shares outstanding as of March 14, 2025, based on the Company's 10-K filed on March 19, 2025.

5,089,260

The Reporting Persons have not entered into any transactions in the Common Stock during the past sixty days, except as set forth below: Buy/Sell Trade Price Quantity Trade Date Buy $2.69 198,262 3/3/25 Buy $2.47 1,000,000 3/4/25 Buy $2.55 250,000 3/5/25 Buy $2.64 350,000 3/6/25 Buy $2.68 250,000 3/7/25 Buy $2.59 225,000 3/10/25 Buy $2.66 310,631 3/11/25 Buy $2.73 9,648 3/12/25 Buy $2.71 160,000 3/13/25 Buy $2.73 28,083 3/14/25 Buy $2.73 15,852 3/17/25 Buy $2.74 16,409 3/18/25 Buy $2.51 153,367 3/26/25 Buy $2.62 20,254 3/27/25 Sell $2.57 40,923 4/4/25 Sell $2.57 77,999 4/4/25 Sell $2.41 1,700 4/7/25 Buy $2.18 198,422 4/14/25 Buy $2.20 144,670 4/15/25 Buy $2.21 173,190 4/16/25 Buy $2.21 300,000 4/17/25 Buy $2.20 32,876 4/17/25 Buy $2.29 2,513 4/22/25 Buy $2.16 64,899 4/24/25 Buy $2.15 17,662 4/25/25 Buy $2.10 45,394 4/25/25 Buy $2.18 42,423 4/28/25 Buy $2.26 35,043 4/29/25 Buy $2.42 10,150 4/30/25

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99.1 - Joint Filing Agreement