Sec Form 3 Filing - ADAR1 Capital Management, LLC @ Keros Therapeutics, Inc. - 2025-04-08

FORM 3 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) 04/08/2025 (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 Common Stock 3,474,844 I By ADAR1 Partners, LP ( 1 ) ( 11 ) Common Stock 254,669 I By ADAR1 SPV I, LP ( 2 ) ( 11 ) Common Stock 727,193 I By Spearhead Insurance Solutions IDF, LLC ( 3 ) ( 11 )

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 02/27/2025 05/16/2025 Common Stock 30,000 I By ADAR1 Partners, LP ( 4 ) ( 11 ) Put Option (obligation to buy) $ 10 04/03/2025 05/16/2025 Common Stock 83,600 I By ADAR1 Partners, LP ( 5 ) ( 11 ) Put Option (obligation to buy) $ 10 04/03/2025 05/16/2025 Common Stock 17,800 I By Spearhead Insurance Solutions IDF, LLC ( 6 ) ( 11 ) Put Option (right to sell) $ 70 10/01/2024 06/20/2025 Common Stock 1,400 I By ADAR1 Partners, LP ( 7 ) ( 11 ) Put Option (right to sell) $ 60 10/02/2024 06/20/2025 Common Stock 100 I By ADAR1 Partners, LP ( 8 ) ( 11 ) Put Option (right to sell) $ 70 10/01/2024 06/20/2025 Common Stock 200 I By Spearhead Insurance Solutions IDF, LLC ( 9 ) ( 11 ) Cash-Settled Total Return Swaps ( 10 ) ( 10 ) 02/02/2026 Common Stock 949,333 I By ADAR1 Partners, LP ( 10 ) ( 11 )

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 /s/ Daniel Schneeberger, Manager 04/11/2025 Signature of Reporting Person Date ADAR1 Partners, LP, By /s/ Daniel Schneeberger, Manager 04/11/2025 Signature of Reporting Person Date ADAR1 Capital Management GP, LLC, By /s/ Daniel Schneeberger, Manager 04/11/2025 Signature of Reporting Person Date /s/ Daniel Schneeberger 04/11/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )ADAR1 Partners, LP is a direct beneficial owner 3,474,844 shares of Common Stock of the Issuer. As the investment manager of ADAR1 Partners, LP, ADAR1 Capital Man agement, LLC may be deemed to be an indirect beneficial owner of such shares. As the general partner of ADAR1 Partners, LP, ADAR1 Capital Management GP, LLC may be deemed to be the indirect beneficial owner of such shares. As the manager of ADAR1 Capital Management, LLC and ADAR1 Capital Management GP, LLC, Daniel Schneeberger may be deemed to be the indirect beneficial owner of such shares. ( 2 )ADAR1 SPV I, LP is a direct beneficial owner 254,669 shares of Common Stock of the Issuer. As the investment manager of ADAR1 SPV I, LP, ADAR1 Capital Management, LLC may be deemed to be an indirect beneficial owner of such shares. As the general partner of ADAR1 SPV I, LP, ADAR1 Capital Management GP, LLC may be deemed to be the indirect beneficial owner of such shares. As the manager of ADAR1 Capital Management, LLC and ADAR1 Capital Management GP, LLC, Daniel Schneeberger may be deemed to be the indirect beneficial owner of such shares. ( 3 )Spearhead Insurance Solutions IDF, LLC is a direct beneficial owner 727,193 shares of Common Stock of the Issuer. As the sub-advisor of Spearhead Insurance Solutions IDF, LLC, ADAR1 Capital Management, LLC may be deemed to be an indirect beneficial owner of such shares. As the manager of ADAR1 Capital Management, LLC, Daniel Schneeberger may be deemed to be the indirect beneficial owner of such shares. ( 4 )ADAR1 Partners, LP is party to put option contracts that provide for an obligation to buy 30,000 shares of Common Stock of the Issuer, if such put options are exercised by the counterparties to such put options. As the investment manager of ADAR1 Partners, LP, ADAR1 Capital Management, LLC may be deemed to be an indirect beneficial owner of such put options. As the general partner of ADAR1 Partners, LP, ADAR1 Capital Management GP, LLC may be deemed to be the indirect beneficial owner of such put options. As the manager of ADAR1 Capital Management, LLC and ADAR1 Capital Management GP, LLC, Daniel Schneeberger may be deemed to be the indirect beneficial owner of such put options. ( 5 )ADAR1 Partners, LP is party to put option contracts that provide for an obligation to buy 83,600 shares of Common Stock of the Issuer, if such put options are exercised by the counterparties to such put options. As the investment manager of ADAR1 Partners, LP, ADAR1 Capital Management, LLC may be deemed to be an indirect beneficial owner of such put options. As the general partner of ADAR1 Partners, LP, ADAR1 Capital Management GP, LLC may be deemed to be the indirect beneficial owner of such put options. As the manager of ADAR1 Capital Management, LLC and ADAR1 Capital Management GP, LLC, Daniel Schneeberger may be deemed to be the indirect beneficial owner of such put options. ( 6 )Spearhead Insurance Solutions IDF, LLC is party to put option contracts that provide for an obligation to buy 17,800 shares of Common Stock of the Issuer, if such put options are exercised by the counterparties to such put options. As the sub-advisor of Spearhead Insurance Solutions IDF, LLC, ADAR1 Capital Management, LLC may be deemed to be an indirect beneficial owner of such put options. As the manager of ADAR1 Capital Management, LLC, Daniel Schneeberger may be deemed to be the indirect beneficial owner of such put options. ( 7 )ADAR1 Partners, LP is a direct beneficial owner of fourteen put options, each with a right to sell 100 shares of Common Stock of the Issuer, exercisable by ADAR1 Partners, LP in its discretion. As the investment manager of ADAR1 Partners, LP, ADAR1 Capital Management, LLC may be deemed to be an indirect beneficial owner of such put options. As the general partner of ADAR1 Partners, LP, ADAR1 Capital Management GP, LLC may be deemed to be the indirect beneficial owner of such put options. As the manager of ADAR1 Capital Management, LLC and ADAR1 Capital Management GP, LLC, Daniel Schneeberger may be deemed to be the indirect beneficial owner of such put options. ( 8 )ADAR1 Partners, LP is a direct beneficial owner of one put option, with a right to sell 100 shares of Common Stock of the Issuer, exercisable by ADAR1 Partners, LP in its discretion. As the investment manager of ADAR1 Partners, LP, ADAR1 Capital Management, LLC may be deemed to be an indirect beneficial owner of such put option. As the general partner of ADAR1 Partners, LP, ADAR1 Capital Management GP, LLC may be deemed to be the indirect beneficial owner of such put option. As the manager of ADAR1 Capital Management, LLC and ADAR1 Capital Management GP, LLC, Daniel Schneeberger may be deemed to be the indirect beneficial owner of such put option. ( 9 )Spearhead Insurance Solutions IDF, LLC is a direct beneficial owner of two put options, each with a right to sell 100 shares of Common Stock of the Issuer, exercisable by Spearhead Insurance Solutions IDF, LLC in its discretion. As the sub-advisor of Spearhead Insurance Solutions IDF, LLC, ADAR1 Capital Management, LLC may be deemed to be an indirect beneficial owner of such put options. As the manager of ADAR1 Capital Management, LLC, Daniel Schneeberger may be deemed to be the indirect beneficial owner of such put option. ( 10 )ADAR1 Partners, LP previously entered into certain cash-settled total return swap agreements with an unaffiliated third-party financial institution, which as of the close of business on April 8, 2025, provide ADAR1 Partners, LP with economic exposure to an aggregate of 949,333 notional shares of Common Stock of the Issuer. The swap agreements provide the ADAR1 Partners, LP with economic results that are comparable to the economic results of ownership but do not provide ADAR1 Partners, LP with the power to vote or direct the voting or dispose of or direct the disposition of the shares of common stock that are the subject of the swap agreements (the "Subject Shares"). Each of the Reporting Persons disclaims beneficial ownership of the Subject Shares except to the extent of its or his pecuniary interest therein. ( 11 )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.

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