MBX Biosciences files Form 4 for 8,000-share director option grant

Rhea-AI Filing Summary

MBX Biosciences, Inc. (MBX) disclosed a new equity award to a director. On 11/22/2025, the director received a stock option to purchase 8,000 shares of common stock at an exercise price of $27.08 per share, reported as a derivative security in Table II.

The option covers 8,000 underlying shares of common stock and is held directly by the reporting person. According to the footnote, the grant will vest in equal monthly installments over a one-year period from November 6, 2025, conditioned on the non-employee director continuing to provide services to the company.

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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hours per response:			0.5

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^*

Hoerter Steven L.

(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
	Officer (give title below)		Other (specify below)

3. Date of Earliest Transaction (Month/Day/Year)
11/22/2025

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

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)	$27.08	11/22/2025		A		8,000		(1)	11/21/2035	Common Stock	8,000	$0	8,000	D

Explanation of Responses:

1. The grant will vest in equal monthly installments over a one-year period from November 6, 2025, subject to the non-employee director's continued services to the Company.

	/s/ Richard Bartram, attorney-in-fact	11/25/2025
	** 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.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

What equity award was reported for MBX Biosciences (MBX)?

A director of MBX Biosciences, Inc. received a stock option classified as a derivative security, covering 8,000 shares of the company’s common stock.

What is the exercise price of the new MBX Biosciences stock option grant?

The stock option granted to the MBX Biosciences director has an exercise price of $27.08 per share.

When was the MBX Biosciences director stock option granted and when does it vest?

The option grant date is 11/22/2025, and it vests in equal monthly installments over a one-year period starting on November 6, 2025, subject to continued service.

How many MBX Biosciences shares underlie the reported stock option?

The reported stock option is exercisable for 8,000 shares of MBX Biosciences common stock, as indicated in Table II.

Is the MBX Biosciences stock option held directly or indirectly by the reporting person?

The filing shows the reporting person holds 8,000 derivative securities directly, corresponding to 8,000 underlying shares of common stock.

What service condition applies to the MBX Biosciences director option vesting?

The vesting of the option is conditioned on the non-employee director’s continued services to MBX Biosciences over the one-year vesting period.