Climb Bio, Inc. — Director's Dealing 2025

Dec 16, 2025

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: Climb Bio, Inc. (CLYM)
CIK: 0001768446
Period of Report: 2025-12-11

Reporting Person: RA CAPITAL MANAGEMENT, L.P. (N/A)
Reporting Person: RA Capital Healthcare Fund LP (Director, 10% Owner)
Reporting Person: RA Capital Nexus Fund, L.P. (Director)
Reporting Person: RA Capital Nexus Fund II, L.P. (Director)
Reporting Person: RA Capital Nexus Fund III, L.P. (Director, 10% Owner)
Reporting Person: Kolchinsky Peter (Director, 10% Owner)
Reporting Person: Shah Rajeev M. (Director, 10% Owner)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2025-12-11	Common Stock	D	20440000	—	Disposed	3081757	Indirect
2025-12-11	Common Stock	P	213099	$2.18	Acquired	3294856	Indirect
2025-12-12	Common Stock	P	101462	$2.86	Acquired	3396318	Indirect

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2025-12-11	Pre-Funded Warrants (Right to Buy)	$0.0001	A	20440000	Acquired		Common Stock (20440000)	Indirect

Holdings (Non-Derivative)

Security	Shares	Ownership
Common Stock	2479872	Indirect
Common Stock	1226497	Indirect
Common Stock	483679	Indirect
Common Stock	2866375	Indirect
Common Stock	841087	Indirect

Footnotes

F1: 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.

F2: These securities are held directly by RA Capital Healthcare Fund, L.P. (the "Fund").

F3: 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.

F4: 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.

F5: 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.

F6: These securities are held directly by Sera.

F7: These securities are held directly by the Nexus Fund.

F8: These securities are held directly by the Nexus Fund II.

F9: These securities are held directly by Nexus Fund III.

F10: These securities are held directly by the Account.

F11: 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.