144 0002030246 XXXXXXXX LIVE 0001776111 MBX Biosciences, Inc. 001-42272 11711 N. MERIDIAN STREET SUITE 300 CARMEL IN 46032 3179893100 Azoulay Salomon Officer Common Fidelity Brokerage Services LLC

900 Salem Street Smithfield RI 02917

70003 2685678.84 47597536 05/08/2026 NASDAQ Common 05/08/2026 Option Granted - 09/12/2024 Issuer N 15003 05/08/2026 Cash Common 05/08/2026 Option Granted - 08/02/2024 Issuer N 55000 05/08/2026 Cash N Salomon Azoulay

11711 N. Meridian Street Suite 300 Carmel IN 46032

Common 05/06/2026 231 6824.78 05/08/2026 01/27/2026 /s/ Emily Navaro, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Salomon Azoulay.