X0609 4 2026-06-04 0001776111 MBX Biosciences, Inc. MBX 0001533451 Hoerter Steven L. false C/O MBX BIOSCIENCES INC. 11711 N. MERIDIAN STREET, SUITE 300 CARMEL IN 46032 true false false false false Common Stock 11938 D Common Stock 20000 I Trust Stock option (right to buy) 30.91 2026-06-04 4 A false 12500 0 A 2036-06-04 Common Stock 12500 12500 D Shares held by the Steven L Hoerter Revocable Trust dated November 2, 2018, of which the Reporting Person serves as trustee. The Reporting Person disclaims beneficial ownership except to the extent of any pecuniary interest therein, and this report shall not be deemed an admission that such shares are beneficially owned by him for Section 16 or any other purpose. The grant will vest in full on the earlier of the one-year anniversary of the grant date or on the date of our next annual meeting of stockholders, subject to the non-employee director's continued services to the Company. /s/ P. Kent Hawryluk, attorney-in-fact 2026-06-05