Sec Form 4 Filing - ADAR1 Capital Management, LLC @ Keros Therapeutics, Inc. - 2025-05-16

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 ADAR1 Capital Management, LLC 2. Issuer Name and Ticker or Trading Symbol Keros Therapeutics, Inc. [ KROS] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 3503 WILD CHERRY DRIVE, BUILDING 9 3. Date of Earliest Transaction (MM/DD/YY) 05/16/2025 (Street) AUSTIN, TX78738 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ 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 Put Option (obligation to buy) $ 10 05/16/2025 E 300 02/27/2025 05/16/2025 Common Stock 30,000 $ 0 0 I By ADAR1 Partners, LP ( 1 ) ( 2 ) Put Option (obligation to buy) $ 10 05/16/2025 E 836 04/03/2025 05/16/2025 Common Stock 83,600 $ 0 0 I By ADAR1 Partners, LP ( 1 ) ( 2 ) Put Option (obligation to buy) $ 10 05/16/2025 E 178 04/03/2025 05/16/2025 Common Stock 17,800 $ 0 0 I By Spearhead Insurance Solutions IDF, LLC ( 1 ) ( 2 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other ADAR1 Capital Management, LLC 3503 WILD CHERRY DRIVE, BUILDING 9 AUSTIN, TX78738 X ADAR1 Partners, LP 3503 WILD CHERRY DRIVE, BUILDING 9 AUSTIN, TX78738 X ADAR1 Capital Management GP, LLC 3503 WILD CHERRY DRIVE, BUILDING 9 AUSTIN, TX78738 X Schneeberger Daniel 3503 WILD CHERRY DRIVE, BUILDING 9 AUSTIN, TX78738 X Signatures ADAR1 Capital Management, LLC, By: Daniel Schneeberger, Manager /s/ Daniel Schneeberger 06/12/2025 Signature of Reporting Person Date ADAR1 Partners, LP, By: Daniel Schneeberger, Manager /s/ Daniel Schneeberger 06/12/2025 Signature of Reporting Person Date ADAR1 Capital Management GP, LLC, By: Daniel Schneeberger, Manager /s/ Daniel Schneeberger 06/12/2025 Signature of Reporting Person Date /s/ Daniel Schneeberger 06/12/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )As the investment manager of ADAR1 Partners, LP and as the sub-advisor of Spearhead Insurance Solutions IDF, LLC, ADAR1 Capital Management, LLC may be deemed to indirectly beneficially own securities held by ADAR1 Partners, LP and Spearhead Insurance Solutions IDF, LLC. As the general partner of ADAR1 Partners, LP, ADAR1 Capital Management GP, LLC may be deemed to indirectly beneficially own securities held by ADAR1 Partners, LP. As the manager of ADAR1 Capital Management, LLC and ADAR1 Capital Management GP, LLC, Mr. Schneeberger may be deemed to indirectly beneficially own securities held by ADAR1 Partners, LP and Spearhead Insurance Solutions IDF, LLC. ( 2 )For purposes of Section 16 of the Securities Exchange Act of 1934, as amended, each Reporting Person disclaims beneficial ownership of any such securities, except to the extent of his/its pecuniary interest therein, if any, and this report shall not be deemed an admission that such Reporting Person is the beneficial owner of such securities for purposes of Section 16 or otherwise.

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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