Material Agreement, Private Placement (Form 8-K)

On December 11, 2025, Climb Bio, Inc. (the "Company") entered into an exchange agreement (the "Exchange Agreement") with RA Capital Management, L.P. ("RA Capital") and an entity affiliated with RA Capital (the "Exchanging Stockholder"), pursuant to which the Exchanging Stockholder agreed to exchange (the "Exchange") an aggregate of 20,440,000 shares of the Company's common stock, par value $0.0001 per share (the "Common Stock"), beneficially owned by the Exchanging Stockholder in consideration for a pre-fundedwarrant (the "Pre-FundedWarrant") to purchase an aggregate of 20,440,000 shares of Common Stock (the "Pre-FundedWarrant Shares") (subject to adjustment in the event of stock splits, recapitalizations and other similar events affecting the Common Stock), with an exercise price of $0.0001 per share. The Pre-FundedWarrant will be exercisable at any time after the date of issuance. The Pre-FundedWarrant Shares are being issued without registration under the Securities Act of 1933, as amended (the "Securities Act"), in reliance on the exemption provided by Section 3(a)(9) of the Securities Act. The transactions contemplated by the Exchange Agreement are expected to close on December 11, 2025, subject to customary closing conditions. Immediately following the consummation of the transactions contemplated by the Exchange Agreement and retirement of the exchanged shares, there will be 47,744,435 shares of Common Stock issued and outstanding. After giving effect to the Exchange, RA Capital, the Exchanging Stockholder and their respective affiliates will beneficially own Common Stock representing approximately 23.0% of the outstanding voting power of the Company.

In accordance with the terms of the Exchange Agreement, RA Capital and the Exchanging Stockholder have agreed to, and to cause each other account or fund managed by or affiliated with RA Capital to, vote all securities beneficially owned by them or their respective affiliates in excess of 33.0% of the total voting power of the outstanding capital stock of the Company, in proportion to and in accordance with the vote of all stockholders of the Company (excluding RA Capital and the Exchanging Stockholder and their respective affiliates). In addition, following the date of the Exchange Agreement, RA Capital may exchange additional shares of Common Stock beneficially owned by it or its affiliates for Pre-FundedWarrants, subject to certain terms and conditions, including the Company's written consent.

The Exchanging Holder will not be entitled to exercise any portion of the Pre-FundedWarrant if, upon giving effect or immediately prior to such exercise, such exercise would result in the aggregate number of shares of Common Stock beneficially owned by RA Capital, the Exchanging Holder and their respective affiliates, collectively, to exceed 33.00% of the number of shares of Common Stock issued and outstanding immediately after giving effect to such exercise, as such percentage ownership is determined in accordance with the terms of the Pre-FundedWarrant. The Exchanging Holder may increase or decrease such percentage to any other percentage not in excess of 33.00%; provided that any such increase will not be effective until the 61st day after notice from the Exchanging Holder is delivered to the Company.

The foregoing descriptions of the form of Pre-FundedWarrant and the Exchange Agreement are not complete and are qualified in their entirety by reference to the full text of the documents, copies of which are filed as Exhibits 4.1 and 10.1, respectively, to this Current Report on Form 8-Kand are incorporated by reference herein. The representations, warranties and covenants made by the Company in the Exchange Agreement and the Pre-FundedWarrant were made solely for the benefit of the parties to the Exchange Agreement and the Pre-FundedWarrant, as applicable, including, in some cases, for the purpose of allocating risk among the parties thereto, and should not be deemed to be a representation, warranty or covenant to investors. Moreover, such representations, warranties or covenants were made as of an earlier date. Accordingly, such representations, warranties and covenants should not be relied on as accurately representing the current state of the Company's affairs.

The description of the transactions contemplated by the Exchange Agreement and the description of the Pre-FundedWarrant described in Item 1.01 are incorporated herein.