Statement of Changes in Beneficial Ownership (Form 4)

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b). Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

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

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1. Name and Address of Reporting Person * RA CAPITAL MANAGEMENT, L.P. 2. Issuer Name and Ticker or Trading Symbol Climb Bio, Inc. [CLYM] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 200 BERKELEY STREET, 18TH FLOOR, 3. Date of Earliest Transaction (Month/Day/Year) 12/11/2025 (Street) BOSTON, MA 02116 4. If Amendment, Date Original Filed (Month/Day/Year) 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 (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 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 12/11/2025 D(1) 20,440,000 D $ 0 3,081,757 I See footnotes(2)(3) Common Stock 12/11/2025 P 213,099 A $2.18(4) 3,294,856 I See footnotes(2)(3) Common Stock 12/12/2025 P 101,462 A $2.86(5) 3,396,318 I See footnotes(2)(3) Common Stock 2,479,872 I See footnotes(3)(6) Common Stock 1,226,497 I See footnotes(3)(7) Common Stock 483,679 I See footnotes(3)(8) Common Stock 2,866,375 I See footnotes(3)(9) Common Stock 841,087 I See footnotes(3)(10)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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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 (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

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 (Month/Day/Year)

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

Pre-Funded Warrants (Right to Buy)

$0.0001

12/11/2025

A(1)

20,440,000

(11)

(11)

Common Stock

20,440,000

(1)

20,440,000

I

See footnotes(2)(3)

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
RA CAPITAL MANAGEMENT, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA 02116	X	X
RA Capital Healthcare Fund LP 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA 02116	X	X
RA Capital Nexus Fund, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA 02116	X
RA Capital Nexus Fund II, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA 02116	X
RA Capital Nexus Fund III, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA 02116	X	X
Kolchinsky Peter C/O RA CAPITAL MANAGEMENT, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA 02116	X	X
Shah Rajeev M. C/O RA CAPITAL MANAGEMENT, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA 02116	X	X

Signatures

/s/ Peter Kolchinsky, Manager of RA Capital Management, L.P.		12/15/2025
**Signature of Reporting Person		Date
/s/ Peter Kolchinsky, Manager of RA Capital Healthcare Fund GP, LLC the General Partner of RA Capital Healthcare Fund, L.P.		12/15/2025
**Signature of Reporting Person		Date
/s/ Peter Kolchinsky, Manager of RA Capital Nexus Fund GP, LLC, the General Partner of RA Capital Nexus Fund, L.P.		12/15/2025
**Signature of Reporting Person		Date
/s/ Peter Kolchinsky, Manager of RA Capital Nexus Fund II GP, LLC, the General Partner of RA Capital Nexus Fund II, L.P.		12/15/2025
**Signature of Reporting Person		Date
/s/ Peter Kolchinsky, Manager of RA Capital Nexus Fund III GP, LLC, the General Partner of RA Capital Nexus Fund III, L.P.		12/15/2025
**Signature of Reporting Person		Date
/s/ Peter Kolchinsky, individually		12/15/2025
**Signature of Reporting Person		Date
/s/ Rajeev Shah, individually		12/15/2025
**Signature of Reporting Person		Date

Explanation of Responses:

*	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).
(1)	On December 11, 2025, RA Capital Healthcare Fund, L.P. (the "Fund") entered into an Exchange Agreement with the Issuer pursuant to which the Fund exchanged, for no additional consideration, 20,440,000 shares of the Issuer's Common Stock for a pre-funded warrant exercisable for up to 20,440,000 shares of the Issuer's Common Stock at an exercise price of $0.0001 per share.
(2)	These securities are held directly by RA Capital Healthcare Fund, L.P. (the "Fund").
(3)	RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus II Fund, L.P. (the "Nexus Fund II"), RA Capital Nexus III Fund, L.P. (the "Nexus Fund III") and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Fund and the Nexus Fund III collectively own approximately 75% of the outstanding equity interests of Sera Medicines, LLC ("Sera"). Accordingly, each of the Fund, the Nexus Fund III and the Adviser may be deemed to beneficially own the securities held by Sera. The Adviser, the Adviser GP, the Fund, the Nexus Fund, the Nexus Fund II, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of the reported securities, except to the extent of their respective pecuniary interest therein.
(4)	The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $2.11 to $2.20 inclusive. The Reporting Persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range set forth in this footnote.
(5)	The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $2.32 to $3.00 inclusive. The Reporting Persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range set forth in this footnote.
(6)	These securities are held directly by Sera.
(7)	These securities are held directly by the Nexus Fund.
(8)	These securities are held directly by the Nexus Fund II.
(9)	These securities are held directly by Nexus Fund III.
(10)	These securities are held directly by the Account.
(11)	The Pre-Funded Warrants have no expiration date and are exercisable immediately. Notwithstanding the foregoing, the Reporting Persons shall not be entitled to exercise the Pre-Funded Warrant if it would cause the aggregate number of shares of Common Stock beneficially owned by the Reporting Persons, their affiliates and any persons who are members of a Section 13(d) group with the Reporting Persons or their affiliates to exceed 33.0% of the total number of issued and outstanding shares of Common Stock of the Issuer following such exercise.
Remarks: Dr. Andrew Levin, a Partner and Managing Director of the Adviser, serves on the Issuer's board of directors.

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