MBX Biosciences, Inc. Commitments Disclosure

Leases

In April 2022, the Company entered into an operating lease agreement for a principal executive office in Carmel, Indiana (the “Carmel Lease”). The Carmel Lease commenced in October 2022 and had an initial term of 39 months, a termination date of December 31, 2025, and an option to extend for 36 additional months at the Company’s discretion. The option to extend was not considered reasonably certain as of the lease inception. On May 9, 2025, the Company entered into the first amendment of

the Carmel Lease (the "First Amendment"). Pursuant to the terms of the First Amendment, the leased premises were expanded, and the lease term was extended through December 31, 2028, with an option to extend for 36 additional months at the Company’s discretion. The option to extend is not considered reasonably certain as of date of the First Amendment.

In December 2023, the Company entered into an operating lease agreement for laboratory space in Indianapolis, Indiana (the “Laboratory Lease”). The Laboratory Lease commenced in December 2023 and had a term of 12 months, terminating in December 2024. The Company entered into a new lease for laboratory space in August 2024, commencing in December 2024, and terminating in December 2025. In October 2025, the Company entered into a new operating lease agreement for laboratory space in Indianapolis, Indiana, commencing in December 2025 and terminating in November 2026. All laboratory leases are short-term leases with no corresponding lease liability or right-of-use asset recorded, and lease payments are recognized as expense on a straight-line basis over the lease terms.

The Company has no other operating or finance leases as of December 31, 2025, or December 31, 2024.

Pursuant to ASC 842, the Company evaluated the new terms of the First Amendment of the Carmel Lease and determined the First Amendment should be treated as a lease modification of the existing Carmel Lease. In accordance with the accounting guidance, the Company remeasured the lease liability as of May 9, 2025, the First Amendment commencement date, to reflect the changes in the lease payments and the change in the lease term. This resulted in an increase of $0.6 million to the Company's lease liability and a corresponding increase to its right-of-use asset as shown on the balance sheet as of December 31, 2025.

The Company incurred $0.3 million and $0.2 million of rent expense for the years ended December 31, 2025, and 2024, respectively.

Cash paid for amounts included in the measurement of the Company’s operating lease liability was $0.2 million and $0.2 million for the years ended December 31, 2025, and December 31, 2024, respectively.

License agreement

In January 2024, the Company entered into an amendment (the "Amendment") for the Exclusive License Agreement with Indiana University Research and Technology Corporation (“IURTC”) (the “License Agreement”), to license certain intellectual property arising under the Master Research Agreement with The Trustees of Indiana University (the "Research Agreement"). The Amendment specifies IURTC is entitled to the receipt of additional clinical and regulatory milestones, as defined in the Amendment, up to an aggregate of $9.0 million. Following the execution of the Amendment, future remaining clinical and regulatory milestone payments in the License Agreement and all amendments totaled up to $9.3 million. In the year ended December 31, 2025, the Company paid a $1.0 million milestone payment to IURTC related to the initiation of the Phase 1 clinical trial of MBX 4291. At December 31, 2025, future remaining clinical and regulatory milestone payments in the IURTC License Agreement and all amendments totaled up to $8.3 million. In consideration for the license, the Company paid immaterial licensing fees to IURTC during the and years ended December 31, 2025, and December 31, 2024.

Legal proceedings

The Company is not currently a party to any material legal proceedings. At each reporting date, the Company evaluates whether a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to its legal proceedings.