MBX Biosciences (MBX) CEO adds 18,500 shares via trust purchase

Rhea-AI Filing Summary

MBX Biosciences, Inc. President & CEO P. Kent Hawryluk reported an open-market purchase of 18,500 shares of Common Stock on March 13, 2026, at a weighted average price of $28.4142 per share.

The shares were bought through the P. Kent Hawryluk Revocable Trust, with prices ranging from $28.28 to $28.48 per share. Following this transaction, the trust holds 486,777 shares indirectly, and his direct holdings are reported at 728,274 shares. The filing notes that he disclaims beneficial ownership of the trust shares 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)
03/13/2026

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								728,274	D
Common Stock	03/13/2026		P		18,500	A	$28.4142(1)	486,777	I	By Trust(2)

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

Explanation of Responses:

1. The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $28.28 to $28.48, 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 number of shares purchased at each separate price within the range set forth in this footnote.

2. 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, attorney-in-fact	03/16/2026
	** 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).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
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FAQ

What insider transaction did MBX Biosciences (MBX) report for its CEO?

MBX Biosciences disclosed that President & CEO P. Kent Hawryluk reported an open-market purchase of Common Stock. The Form 4 shows a single buy transaction executed on March 13, 2026, reflecting additional insider exposure to MBX shares through an affiliated trust.

How many MBX shares did CEO P. Kent Hawryluk buy and at what price?

He purchased 18,500 MBX shares in the open market at a weighted average price of $28.4142 per share. The filing explains that individual trades occurred between $28.28 and $28.48, and detailed trade-level prices are available upon request.

How are the newly purchased MBX Biosciences shares held?

The purchased shares are held by the P. Kent Hawryluk Revocable Trust, where he serves as trustee. The Form 4 notes that he disclaims beneficial ownership of these trust-held shares except to the extent of any pecuniary interest, clarifying the indirect nature of this ownership.

What are P. Kent Hawryluk’s reported MBX share holdings after this transaction?

After the reported purchase, the trust associated with him holds 486,777 MBX shares indirectly. The filing also shows 728,274 MBX shares as directly held. Together, these figures outline his total reported direct and indirect positions following the March 13, 2026 transaction.

Was the MBX Biosciences CEO’s share purchase in the open market?

Yes. The Form 4 identifies the transaction as an open-market purchase of Common Stock. It reports a weighted average execution price and notes the underlying trades occurred within a narrow price band between $28.28 and $28.48 per share on March 13, 2026.

Does the MBX CEO fully own the trust-held shares reported in this Form 4?

The filing states that shares are held by the P. Kent Hawryluk Revocable Trust, where he is trustee, and that he disclaims beneficial ownership of those shares except for any pecuniary interest. This language limits how his economic and voting interest in the trust-held shares is characterized.