32,000 MBX Biosciences (MBX) stock options granted to director

Rhea-AI Filing Summary

MBX Biosciences granted director Laurie Stelzer stock options covering 32,000 shares of common stock on January 20, 2026. These options have an exercise price of $43.14 per share and are held as a direct ownership position.

One-third of the underlying shares will vest and become exercisable on January 20, 2027, the first anniversary of the grant date, with the remaining two-thirds vesting monthly over the following two years, subject to her continued service. After this grant, she beneficially owns 32,000 derivative securities linked to MBX Biosciences common stock.

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^*

Stelzer Laurie

(Last) (First) (Middle)

C/O MBX BIOSCIENCES, INC.

11711 N. MERIDIAN STREET, STE 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)
01/20/2026

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

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)	$43.14	01/20/2026		A		32,000		(1)	01/20/2036	Common Stock	32,000	$0	32,000	D

Explanation of Responses:

1. One-third of the shares underlying this option will vest and become exercisable on January 20, 2027, the anniversary of the date of grant, with the remainder vesting monthly over the subsequent two year period, subject to the Reporting Person's continued service on each such vesting date.

	/s/ Richard Bartram, attorney-in-fact	01/22/2026
	** 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.
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 insider transaction did MBX Biosciences (MBX) report in this Form 4?

The filing reports that director Laurie Stelzer received a grant of stock options covering 32,000 shares of MBX Biosciences common stock on January 20, 2026.

How many MBX Biosciences (MBX) stock options were granted to Laurie Stelzer and at what price?

Laurie Stelzer was granted 32,000 stock options, each with an exercise price of $43.14 per share, giving her the right to buy MBX Biosciences common stock at that price once vested.

What is the vesting schedule for Laurie Stelzer’s MBX Biosciences stock options?

According to the footnote, one-third of the shares underlying the option will vest and become exercisable on January 20, 2027, with the remaining shares vesting monthly over the subsequent two years, subject to her continued service.

What is Laurie Stelzer’s relationship to MBX Biosciences (MBX)?

Laurie Stelzer is a director of MBX Biosciences, as indicated in the relationship section of the filing. She is not listed as an officer or 10% owner in this document.

How many MBX Biosciences derivative securities does Laurie Stelzer own after this transaction?

Following the reported grant, Laurie Stelzer beneficially owns 32,000 derivative securities (stock options) linked to MBX Biosciences common stock, held as a direct ownership position.

Is Laurie Stelzer’s stock option holding in MBX Biosciences direct or indirect?

The filing classifies her ownership of the 32,000 stock options as Direct (D), and no indirect ownership entity is noted in the transaction details.