MBX Biosciences, Inc.

Item 5. Other Information.

(a) On May 9, 2025, we entered into a first amendment (the "First Amendment") to our lease, dated April 28, 2022 (the "Carmel Lease"), with Zeller-Carmel Property, LLC, related to our principal executive office.

Pursuant to the terms of the First Amendment, the leased premises are expanded from 6,493 square feet of office space to 8,260 square feet of office space, and the expiration date of the lease is extended from December 31, 2025 to December 31, 2028, with an option to extend for 36 additional months at our discretion. Future minimum rent payments under the First Amendment total $0.7 million.

The foregoing summary of the First Amendment does not purport to be a complete description of the document and is qualified in its entirety by the First Amendment, a copy of which is filed as Exhibit 10.1 to this Quarterly Report on Form 10-Q and incorporated herein by reference.

(c)None of our directors or “officers,” as defined in Rule 16a-1(f) under the Securities Exchange Act of 1934, adopted or terminated a Rule 10b5-1 trading plan or arrangement or a non-Rule 10b5-1 trading plan or arrangement, as defined in Item 408(c) of Regulation S-K, during the fiscal quarter covered by this report.