MBX Biosciences (MBX) CMO sells 370 shares to cover RSU taxes

Rhea-AI Filing Summary

MBX Biosciences, Inc. reported that Chief Medical Officer Salomon Azoulay sold 370 shares of common stock on August 4, 2026 at a weighted average price of $65.77 per share to cover tax obligations from vesting restricted stock units under a mandatory sell-to-cover agreement, leaving 14,399 shares held directly.

Insider Trade Summary

Net Seller: 370 shares

Net Sell 1 txn

Insider Azoulay Salomon

Role Chief Medical Officer

Sold 370 shs ($24K)

Type	Security	Shares	Price	Value
Sale	Common Stock F1, F2	370	$65.77	$24K

Holdings After Transaction: Common Stock — 14,399 shares (Direct)

Footnotes (2)

1. F1. The sales reported on this Form 4 represent shares of common stock sold by the Reporting Person to cover tax obligations in connection with the vesting of restricted stock units, pursuant to a mandatory sell-to-cover agreement between the Reporting Person and the Company.
2. F2. The price reported in Column 4 is a weighted average price. These shares were sold on an aggregate basis for all Company participants, at prices ranging from $65.21 to $66.43, 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 aggregate number of shares sold at each separate price within the range set forth in this footnote.

Key Figures

Shares sold: 370 shares Sale price (weighted average): $65.77 per share Sale price range: $65.21-$66.43 per share +1 more

4 metrics

Shares sold 370 shares Common Stock sale on 2026-08-04 by Chief Medical Officer

Sale price (weighted average) $65.77 per share Weighted average price reported for the shares sold

Sale price range $65.21-$66.43 per share Aggregate price range for sales covering all company participants

Shares owned after transaction 14,399 shares Directly held MBX Biosciences common shares after the sale

Key Terms

sell-to-cover agreement, restricted stock units, weighted average price

3 terms

sell-to-cover agreement financial

"pursuant to a mandatory sell-to-cover agreement between the Reporting Person and the Company"

restricted stock units financial

"tax obligations in connection with the vesting of restricted stock units"

Restricted stock units are a type of company reward where employees are promised shares of stock, but they only fully own these shares after meeting certain conditions, like staying with the company for a set time. They matter because they can become valuable assets and are often used to motivate employees to help the company succeed.

weighted average price financial

"The price reported in Column 4 is a weighted average price."

Weighted average price is the average price of a security where each trade or component is counted according to its size, so bigger trades pull the average more than smaller ones. Think of it like calculating the average cost of a grocery haul where items you bought more of have greater influence on the final per-item cost. Investors use it to understand the true average price paid or received, judge execution quality, and compare trading performance against market movement.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Form 4 Insider Transactions: What Each Field Means →

Available on EDGAR 08/05/2026 - 04:57 PM Accepted by SEC EDGAR 08/05/2026 - 04:57 PM Learn about SEC filing dates

FAQ

What insider transaction did MBX Biosciences (MBX) report in this Form 4?

MBX Biosciences reported that Chief Medical Officer Salomon Azoulay sold 370 shares of common stock on August 4, 2026 at a weighted average price of $65.77 per share, leaving him with 14,399 shares of direct ownership.

Why did MBX Biosciences (MBX) Chief Medical Officer sell 370 shares?

The filing states the 370-share sale was made to cover tax obligations arising from the vesting of restricted stock units, under a mandatory sell-to-cover agreement between Salomon Azoulay and MBX Biosciences, rather than as a discretionary open-market sale.

How many MBX (MBX) shares does the Chief Medical Officer own after the sale?

Following the reported transaction, Chief Medical Officer Salomon Azoulay directly holds 14,399 shares of MBX Biosciences common stock. This figure is disclosed as the total number of shares beneficially owned after the 370-share tax-related sale on August 4, 2026.

At what prices were the MBX Biosciences (MBX) shares sold in this transaction?

The reported per-share price of $65.77 is a weighted average price. According to the footnote, the shares for all company participants were sold at prices ranging from $65.21 to $66.43 per share in aggregate transactions.

Was the MBX Biosciences (MBX) CMO’s sale made under a trading plan?

The Rule 10b5-1 checkbox is not marked. Instead, the sale is described as occurring under a mandatory sell-to-cover agreement with MBX Biosciences to satisfy tax obligations from vesting restricted stock units, as stated in the footnotes.

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^*

Azoulay Salomon

(Last) (First) (Middle)

C/O MBX BIOSCIENCES, INC.

11711 N. MERIDIAN STREET, SUITE 300

(Street)

CARMEL INDIANA 46032

(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)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Chief Medical Officer

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
08/04/2026

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
Common Stock	08/04/2026		S		370(1)	D	$65.77(2)	14,399	D

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 sales reported on this Form 4 represent shares of common stock sold by the Reporting Person to cover tax obligations in connection with the vesting of restricted stock units, pursuant to a mandatory sell-to-cover agreement between the Reporting Person and the Company.

2. The price reported in Column 4 is a weighted average price. These shares were sold on an aggregate basis for all Company participants, at prices ranging from $65.21 to $66.43, 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 aggregate number of shares sold at each separate price within the range set forth in this footnote.

Remarks:

Exhibit 24 - Power of Attorney

	/s/ John W. Smither	08/05/2026
	** 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)