X0609 4 2026-08-03 0001776111 MBX Biosciences, Inc. MBX 0001559583 Smither John W false 11711 N. MERIDIAN STREET SUITE 300 CARMEL IN 46032 false true false false Chief Financial Officer false Common Stock 2026-08-03 4 A false 28000 0 A 28000 D Stock option (right to buy) 64.41 2026-08-03 4 A false 130000 0 A 2036-08-03 Common Stock 130000 130000 D Represents the grant of restricted stock units ("RSUs"). 25% of the shares subject to the RSU grant will vest annually over four years, on each July 13, 2027, 2028, 2029 and 2030, subject to continued service on each such vesting date. The options will vest and become exercisable with 25% of the shares subject to the award vesting on July 13, 2027 and the remainder vesting in 36 equal monthly installments thereafter, subject to continued service on each such vesting date. Exhibit 24 - Power of Attorney /s/ John W. Smither 2026-08-04