P. Kent Hawryluk - 24 Oct 2025 Form 4 Insider Report for MBX Biosciences, Inc. (MBX)

Role: President & CEO, Director
Signature: /s/ Richard Bartram, attorney-in-fact
Issuer symbol: MBX
Transactions as of: 24 Oct 2025
Net transactions value: +$594,292
Form type: 4
Filing time: 28 Oct 2025, 08:03:15 UTC
Previous filing: 21 Oct 2025
Next filing: 03 Feb 2026
SEC: View on sec.gov

Reporting Owners (1)

Name	Relationship	Address	Signature	Signature date	CIK
Hawryluk P. Kent	President & CEO, Director	C/O MBX BIOSCIENCES, INC., 11711 N. MERIDIAN STREET, SUITE 300, CARMEL	/s/ Richard Bartram, attorney-in-fact	28 Oct 2025	0001673991

Transactions Table

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Ownership	Footnotes
transaction	MBX	Common Stock	Options Exercise	$594,292	+182,859	+38%	$3.25	664,256	24 Oct 2025	Direct
holding	MBX	Common Stock						468,277	24 Oct 2025	By Trust	F1

Derivative Securities (e.g., puts, calls, warrants, options, convertible securities)

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Underlying Class	Amount	Exercise Price	Ownership	Footnotes
transaction	MBX	Stock option (right to buy)	Options Exercise	$0	-182,859	-59%	$0.000000	129,708	24 Oct 2025	Common Stock	182,859	$3.25	Direct	F2

* An asterisk sign (*) next to the price indicates that the price is likely invalid.

Explanation of Responses:

Id	Content
F1	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.
F2	1/48th of the shares underlying this option vest in substantially equal monthly installments on each monthly anniversary of November 7, 2022, subject to the Reporting Person's continued service on each such vesting date, until the option vests in full on November 7, 2026. The shares underlying this option became exercisable in full on November 7, 2022, pursuant to an early-exercise provision, subject to an Issuer right of repurchase.

Content

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.

1/48th of the shares underlying this option vest in substantially equal monthly installments on each monthly anniversary of November 7, 2022, subject to the Reporting Person's continued service on each such vesting date, until the option vests in full on November 7, 2026. The shares underlying this option became exercisable in full on November 7, 2022, pursuant to an early-exercise provision, subject to an Issuer right of repurchase.