EXHIBIT 99.1
JOINT FILING AGREEMENT
Pursuant to Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, the undersigned hereby agree that only one statement containing the information required by Schedule 13D need be filed with respect to the ownership by each of the undersigned of Shares of Common Stock of MBX Biosciences, Inc.
Date: August 10, 2026
FRAZIER LIFE SCIENCES PUBLIC FUND, L.P.
By: FHMLSP, L.P., its General Partner
By: FHMLSP, L.L.C., its General Partner
By: /s/ Jennifer Martin
Jennifer Martin, Chief Financial Officer
Date: August 10, 2026
FHMLSP, L.P.
By: FHMLSP, L.L.C., its General Partner
By: /s/ Jennifer Martin
Jennifer Martin, Chief Financial Officer
Date: August 10, 2026
FHMLSP, L.L.C.
By: /s/ Jennifer Martin
Jennifer Martin, Chief Financial Officer
Date: August 10, 2026
FRAZIER LIFE SCIENCES X, L.P.
By: FHMLS X, L.P., its General Partner
By: FHMLS X, L.L.C., its General Partner
By: /s/ Jennifer Martin
Jennifer Martin, Chief Financial Officer
Date: August 10, 2026
FHMLS X, L.P.
By: FHMLS X, L.L.C., its General Partner
By: /s/ Jennifer Martin
Jennifer Martin, Chief Financial Officer
Date: August 10, 2026
FHMLS X, L.L.C.
By: /s/ Jennifer Martin
Jennifer Martin, Chief Financial Officer
Date: August 10, 2026
FRAZIER LIFE SCIENCES XI, L.P.
By: FHMLS XI, L.P., its General Partner
By: FHMLS XI, L.L.C., its General Partner
By: /s/ Jennifer Martin
Jennifer Martin, Chief Financial Officer
Date: August 10, 2026
FHMLS XI, L.P.
By: FHMLS XI, L.L.C., its General Partner
By: /s/ Jennifer Martin
Jennifer Martin, Chief Financial Officer
Date: August 10, 2026
FHMLS XI, L.L.C.
By: /s/ Jennifer Martin
Jennifer Martin, Chief Financial Officer
Date: August 10, 2026
By: *
James N. Topper
Date: August 10, 2026
By: *
Patrick J. Heron
Date: August 10, 2026
By: /s/ Jennifer Martin
Jennifer Martin, as Attorney-in-Fact
* This Joint Filing Agreement was executed by Jennifer Martin on behalf of the individuals listed above pursuant to a Power of Attorney, a copy of which was filed with the SEC on January 27, 2026.