X0609 4 2026-10-20 false 0001776111 MBX Biosciences, Inc. MBX 0001650131 Radovich Peter false 11711 N. MERIDIAN STREET SUITE 300 CARMEL IN 46032 true false false false false Stock option (right to buy) 53.50 2026-10-20 4 A false 18200 0 A 2036-10-20 Common Stock 18200 18200 D One-third of the shares underlying this option will vest and become exercisable on October 20, 2027, the anniversary of the date of grant, with the remainder vesting monthly over the subsequent two year period, subject to the Reporting Person's continued service on each such vesting date. /s/ Steven L. Hoerter 2026-10-22