Exhibit 1

JOINT FILING AGREEMENT

The undersigned hereby agree that Amendment No. 2 to the Statement on Schedule 13D, dated February 5, 2026, with respect to the common stock, par value $0.0001 per share, of MBX Biosciences, Inc. is filed on behalf of each of us pursuant to and in accordance with the provisions of Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended. Each of the undersigned agrees to be responsible for the timely filing of this Statement, and for the completeness and accuracy of the information concerning itself contained therein. This Joint Filing Agreement may be executed in any number of counterparts, all of which taken together shall constitute one and the same instrument.

IN WITNESS WHEREOF, the undersigned have executed this Joint Filing Agreement as of the 11^th day of February 2026.

	ORBIMED ADVISORS LLC

	By:	/s/ Carl L. Gordon
		Name: Carl L. Gordon
		Title: Member

	ORBIMED CAPITAL GP VII LLC

	By:	ORBIMED ADVISORS LLC, its managing member

	By:	/s/ Carl L. Gordon
		Name: Carl L. Gordon
		Title: Member of OrbiMed Advisors LLC

	ORBIMED GENESIS GP LLC

	By:	ORBIMED ADVISORS LLC, its managing member

	By:	s/ Carl L. Gordon
		Name: Carl L. Gordon
		Title: Member of OrbiMed Advisors LLC

MBX Biosciences, Inc. SCHEDULE 13D/A