MBX Biosciences (MBX) CEO exercises stock options into 28,768 shares

Rhea-AI Filing Summary

MBX Biosciences, Inc. director and President & CEO P. Kent Hawryluk reported exercising stock options into common stock. On February 26, 2026, he exercised options covering 28,768 shares, with the resulting common stock recorded at $16.00 per share.

After these transactions, his directly held common stock position is 728,274 shares, and directly held stock options total 91,668 shares underlying options. An additional 468,277 common shares are held indirectly by the P. Kent Hawryluk Revocable Trust, where he serves as trustee and disclaims beneficial ownership except for any pecuniary interest.

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
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Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Hawryluk P. Kent

(Last) (First) (Middle)

C/O MBX BIOSCIENCES, INC.

11711 N. MERIDIAN STREET, SUITE 300

(Street)

CARMEL IN 46032

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
MBX Biosciences, Inc. [ MBX ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	President & CEO

3. Date of Earliest Transaction (Month/Day/Year)
02/26/2026

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	02/26/2026		M		28,768	A	$16	728,274	D
Common Stock								468,277	I	By Trust(1)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Stock option (right to buy)	$16	02/26/2026		M			28,768	(2)	09/12/2034	Common Stock	28,768	$0	91,668	D

Explanation of Responses:

1. 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.

2. 25% of the shares underlying this option vested and became exercisable on September 12, 2025, with the remaining 75% vesting in thirty-six (36) equal monthly installments thereafter, subject to the Reporting Person's continued service on each such vesting date.

	/s/ Richard Bartram, attorney-in-fact	02/27/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
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FAQ

What insider transaction did MBX CEO P. Kent Hawryluk report?

P. Kent Hawryluk reported exercising stock options into MBX common stock. On February 26, 2026, he exercised options for 28,768 shares, with the resulting common stock recorded at $16.00 per share, increasing his directly held MBX equity exposure.

How many MBX shares does CEO P. Kent Hawryluk hold directly after this Form 4?

Following the reported transactions, P. Kent Hawryluk directly holds 728,274 shares of MBX common stock. He also directly holds stock options covering 91,668 shares, reflecting his equity-based compensation and alignment with MBX Biosciences’ long-term performance.

What stock options did MBX Biosciences’ CEO exercise in this filing?

The CEO exercised a stock option for 28,768 underlying shares. The option exercise was recorded at a $16.00 per-share price for the resulting common stock, and the option position after the transaction totals 91,668 shares underlying options held directly.

How many MBX shares are held indirectly through the Hawryluk revocable trust?

An indirect holding of 468,277 MBX common shares is reported as held by the P. Kent Hawryluk Revocable Trust. Hawryluk serves as trustee and disclaims beneficial ownership of these shares except to the extent of any pecuniary interest in the trust.

What does the vesting schedule footnote say about the MBX stock option?

The footnote explains that 25% of the shares underlying the option vested and became exercisable on September 12, 2025, with the remaining 75% vesting in 36 equal monthly installments, contingent on Hawryluk’s continued service through each vesting date.