X0609 4 2026-05-06 0001776111 MBX Biosciences, Inc. MBX 0001673991 Hawryluk P. Kent false C/O MBX BIOSCIENCES, INC. 11711 N. MERIDIAN STREET, SUITE 300 CARMEL IN 46032 true true false false President & CEO false Common Stock 2026-05-06 4 S false 607 29.54 D 727667 D Common Stock 486777 I By Trust The sales reported on this Form 4 represent shares of common stock sold by the Reporting Person to cover tax obligations in connection with the vesting of restricted stock units, pursuant to a mandatory sell-to-cover agreement between the Reporting Person and the Company. The price reported in Column 4 is a weighted average price. These shares were sold on an aggregrate basis for all Company participants, at prices ranging from $29.23 to $29.88, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the aggregrate number of shares sold at each separate price within the range set forth in this footnote. Shares held by the P. Kent Hawryluk Revocable Trust dated January 25, 2011, 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. /s/ P. Kent Hawryluk 2026-05-08