Sec Form 4 Filing - COZADD BRUCE C @ ACELYRIN, Inc. - 2025-05-21

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person COZADD BRUCE C 2. Issuer Name and Ticker or Trading Symbol ACELYRIN, Inc. [ SLRN] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O ACELYRIN, INC., 4149 LIBERTY CANYON RD. 3. Date of Earliest Transaction (MM/DD/YY) 05/21/2025 (Street) AGOURA HILLS, CA91301 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Director Stock Option (right to buy) $ 4.0426 05/21/2025 D 183,434 ( 1 ) 03/07/2032 Common Stock 183,434 ( 2 ) ( 3 ) 0 D Director Stock Option (right to buy) $ 18 05/21/2025 D 23,243 ( 4 ) 05/03/2033 Common Stock 23,243 ( 2 ) ( 3 ) 0 D Director Stock Option (right to buy) $ 4.46 05/21/2025 D 92,158 ( 5 ) 06/06/2034 Common Stock 92,158 ( 2 ) ( 3 ) 0 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other COZADD BRUCE C C/O ACELYRIN, INC. 4149 LIBERTY CANYON RD. AGOURA HILLS, CA91301 X Signatures /s/ Eddie Kim, Attorney-in-fact 05/23/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )1/48 of the shares subject to the option vested on April 7, 2022, and 1/48 of the shares subject to the option vests in equal monthly installments thereafter, subject to the Reporting Person's continued service. ( 2 )On February 6, 2025, ACELYRIN, Inc., a Delaware corporation (the "Company"), entered into an Agreement and Plan of Merger (as amended on April 20, 2025, the "Merger Agreement") with Alumis, Inc., a Delaware corporation ("Parent"), and Arrow Merger Sub, Inc., a Delaware corporation and wholly owned subsidiary of Parent ("Merger Sub"). Pursuant to the Merger Agreement, on May 21, 2025, Merger Sub merged with and into the Company (the "Merger"), with the Company surviving as a wholly owned subsidiary of Parent. At the effective time of the Merger (the "Effective Time"), each share of common stock, par value $0.00001 per share, of the Company issued and outstanding was converted into the right to receive 0.4814 (the "Exchange Ratio") shares of voting common stock of Parent, par value $0.0001 per share ("Parent Common Stock"), and cash in lieu of any fractional shares. ( 3 )Pursuant to the Merger Agreement, at the Effective Time each stock option that was outstanding and unexercised immediately prior to the Effective Time with a per share exercise price of $18.00 or less was assumed by Parent and converted into an option to purchase a number of shares of Parent Common Stock equal to (i) the number of shares subject to the option immediately prior to the Effective Time, multiplied by (ii) the Exchange Ratio, with any fractional shares rounded down to the nearest whole share, which stock option shall have an exercise price equal to (i) the per share exercise price for shares subject to the corresponding Company stock option immediately prior to the Effective Time, divided by (ii) the Exchange Ratio, rounded up to the nearest whole cent. ( 4 )1/36 of the shares subject to the option vested on June 4, 2023, and 1/36 of the shares subject to the option vest in equal monthly installments thereafter, subject to the Reporting Person's continued service. ( 5 )All of the shares subject to the option vest on the earlier of (i) June 7, 2025, or (ii) the day immediately preceding the next annual meeting of stockholders following the grant date of the option, subject to the Reporting Person's continued service as a director through the vesting date.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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