MBX Biosciences (MBX) director granted 12,500 stock options at $30.91 strike

Rhea-AI Filing Summary

MBX Biosciences director Edward T. Mathers received a new stock option grant covering 12,500 shares of common stock. The option has an exercise price of $30.91 per share and expires on June 4, 2036. Following this grant, he holds 12,500 stock option rights directly.

The grant vests in full on the earlier of the one-year anniversary of the grant date or the date of the company’s next annual meeting of stockholders, as long as he continues serving as a non-employee director.

Insider Trade Summary

1 transaction reported

Mixed 1 txn

Insider Mathers Edward T

Role null

Type	Security	Shares	Price	Value
Grant/Award	Stock option (right to buy)	12,500	$0.00	--

Holdings After Transaction: Stock option (right to buy) — 12,500 shares (Direct, null)

Footnotes (1)

1. [object Object]

Key Figures

Option grant size: 12,500 options Exercise price: $30.91 per share Underlying shares: 12,500 shares +2 more

5 metrics

Option grant size 12,500 options Stock option (right to buy) granted to director

Exercise price $30.91 per share Conversion or exercise price of stock options

Underlying shares 12,500 shares Common stock underlying the options

Expiration date June 4, 2036 Option expiration

Post-grant derivative holdings 12,500 options Total derivative securities following transaction

Key Terms

Stock option (right to buy), exercise price, expiration date, non-employee director, +1 more

5 terms

Stock option (right to buy) financial

"security_title: Stock option (right to buy)"

exercise price financial

"conversion_or_exercise_price: 30.9100"

The exercise price is the fixed amount at which you can buy or sell an asset, like a stock, when using an options contract. It matters because it helps determine whether exercising the option will be profitable or not, depending on the current market price. Think of it as the set price you agree on today to buy or sell later.

expiration date financial

"expiration_date: 2036-06-04T00:00:00.000Z"

The expiration date is the deadline after which a financial contract, such as an option or a futures agreement, is no longer valid or can be exercised. It matters to investors because it determines the timeframe during which they can take action or benefit from the contract, similar to how a coupon or a food item has a limited period of usefulness. Once the expiration date passes, the contract loses its value or ability to be used.

non-employee director financial

"subject to the non-employee director's continued services to the Company"

annual meeting of stockholders financial

"on the date of our next annual meeting of stockholders"

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Form 4 Insider Transactions: What Each Field Means →

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
Estimated average burden
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^*

Mathers Edward T

(Last) (First) (Middle)

104 5TH AVE

19TH FLOOR

(Street)

NEW YORK NEW YORK 10011

(City) (State) (Zip)

UNITED STATES

(Country)

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)

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
06/04/2026

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

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

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

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)	$30.91	06/04/2026		A		12,500		(1)	06/04/2036	Common Stock	12,500	$0	12,500	D

Explanation of Responses:

1. The grant will vest in full on the earlier of the one-year anniversary of the grant date or on the date of our next annual meeting of stockholders, subject to the non-employee director's continued services to the Company.

	/s/ Zachary Bambach, attorney-in-fact	06/05/2026
	** 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.
* Form 4: SEC 1474 (03-26)

FAQ

What did Edward T. Mathers report in his MBX Form 4 filing?

Edward T. Mathers reported receiving a stock option grant for 12,500 MBX common shares. The award is a director compensation grant, not an open-market purchase, and is exercisable at $30.91 per share until June 4, 2036.

What are the terms of Edward T. Mathers’ new MBX stock options?

The new MBX stock options cover 12,500 shares at a $30.91 exercise price. They expire on June 4, 2036 and vest in full based on service conditions tied to one year or the next annual stockholder meeting.

When do Edward T. Mathers’ MBX stock options vest?

The options vest in full on the earlier of the one-year anniversary of the June 4, 2036 grant date or MBX’s next annual stockholder meeting. Vesting requires Mathers to continue serving as a non-employee director until that vesting date.

Is Edward T. Mathers’ MBX Form 4 transaction a market purchase or sale?

The Form 4 transaction is a grant of stock options, not a market trade. It reflects a compensation-related award coded as an acquisition, with no open-market buying or selling of MBX common shares reported in this filing.

How many MBX derivative securities does Edward T. Mathers hold after this grant?

After this grant, Edward T. Mathers holds 12,500 MBX stock option rights directly. Each option is exercisable for one share of common stock at $30.91 per share, subject to vesting and the June 4, 2036 expiration date.