Material Agreement (Form 8-K)

As previously announced, on June 22, 2026, Boundless Bio, Inc., a Delaware corporation ("Boundless Bio"), Boulder Merger Sub Corp., a Delaware corporation and wholly owned subsidiary of Boundless Bio ("Merger Sub"), and Serapha Bio, Inc., a Delaware corporation ("Serapha"), entered into an Agreement and Plan of Merger and Reorganization (as amended, the "Merger Agreement"), pursuant to which Merger Sub will be merged with and into Serapha, with Serapha surviving as a wholly owned subsidiary of Boundless Bio (the "Merger" and, together with all of the other transactions contemplated by the Merger Agreement, the "Contemplated Transactions"). Capitalized terms used but not otherwise defined in this Item 1.01 shall have the meanings ascribed to such terms in the Merger Agreement.

On August 28, 2026, the parties entered into Amendment No. 1 to the Merger Agreement (the "Amendment"). The Amendment amends the Merger Agreement to, among other things, (i) clarify certain definitions and provisions, including in relation to the Company Pre-Closing Financing; (ii) add mechanics for the treatment of Serapha restricted stock unit awards ("Serapha RSUs"), providing that each Serapha RSU (whether vested or unvested) outstanding immediately prior to the effective time of the Merger will be converted into a restricted stock unit award (an "Assumed RSU") covering shares of Boundless Bio common stock, par value $0.0001 per share ("Boundless Bio Common Stock"), on generally the same terms and conditions, with the number of shares subject to each such Assumed RSU adjusted by the Exchange Ratio; (iii) add mechanics for the issuance of pre-funded warrants (with an exercise price of $0.00001 per share) as Merger Consideration in lieu of shares of Boundless Bio Common Stock to the extent the issuance of such shares would cause a holder to exceed its applicable Beneficial Ownership Limitation; and (iv) provide that the voting standard for the increase in the number of authorized shares of Boundless Bio Common Stock is the affirmative vote of a majority of the shares of Boundless Bio Common Stock properly cast, rather than the affirmative vote of a majority of the shares of Boundless Bio Common Stock outstanding and entitled to vote thereon.

Except as modified by the Amendment, the terms of the Merger Agreement in the form filed as Exhibit 2.1 to the Current Report on Form 8-K filed by Boundless Bio on June 23, 2026 with the U.S. Securities and Exchange Commission (the "SEC") are unchanged.

The foregoing description of the Amendment is subject to, and is qualified in its entirety by, the full text of the Amendment filed as Exhibit 2.1 to this Current Report on Form 8-K, which is incorporated herein by reference.