MBX files to sell 1,061 vested shares

MBX files a Section 144 notice to sell 1,061 shares of Common Stock related to Restricted Stock Vesting that occurred on 03/23/2026.

Accepted by SEC EDGAR 03/25/2026 - 03:20 PM EDT Learn about SEC filing dates

Rhea-AI Filing Summary

MBX files a Section 144 notice to sell 1,061 shares of Common Stock related to Restricted Stock Vesting that occurred on 03/23/2026.

The filing also reports a prior disposition by Richard Bartram of 10,000 shares on 03/16/2026 for $300,471. The filing names Fidelity Brokerage Services LLC as the broker and lists an account reference for the proposed sale.

Insights

Insider Transactions Analyst

Routine Section 144 notice for vested shares; prior small insider sale disclosed.

The filing lists the proposed sale of 1,061 shares tied to Restricted Stock Vesting on 03/23/2026. This is a routine, compensation‑related disposition notice by an affiliate and uses a registered broker account at Fidelity Brokerage Services LLC.

It also discloses a prior open disposition of 10,000 shares on 03/16/2026 for $300,471. Cash‑flow treatment for the proposed sale and any transfer restrictions are timing/condition details not included in the excerpt.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What does MBX's Form 144 report about shares to be sold?

The filing reports a proposed sale of 1,061 shares tied to restricted stock vesting on 03/23/2026. The notice lists the sale method through a brokerage account at Fidelity Brokerage Services LLC and identifies the transaction as compensation‑related.

Did any insider recently sell MBX shares?

Yes. The filing shows Richard Bartram disposed of 10,000 shares on 03/16/2026 for $300,471. That prior transaction is reported separately from the new proposed sale tied to vesting.

Who is the broker listed for the proposed MBX sale?

The broker named is Fidelity Brokerage Services LLC with an account reference listed. The filing shows the brokerage as the channel for the proposed sale but does not state execution timing or proceeds recipient beyond the issuer/compensation context.

Is the 1,061‑share amount part of compensation?

Yes. The filing labels the 1,061 shares as resulting from Restricted Stock Vesting and identifies the transaction source as Compensation on 03/23/2026. The entry ties the shares to an issuance event rather than an open‑market purchase.

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

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Form 144 Filer Information	UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Form 144 NOTICE OF PROPOSED SALE OF SECURITIES PURSUANT TO RULE 144 UNDER THE SECURITIES ACT OF 1933
FORM 144

144: Filer Information

Filer CIK	0001723729
Filer CCC	XXXXXXXX
Is this a LIVE or TEST Filing?	LIVE TEST
Submission Contact Information
Name
Phone
E-Mail Address

144: Issuer Information

Name of Issuer	MBX Biosciences, Inc.
SEC File Number	001-42272
Address of Issuer	11711 N. MERIDIAN STREET SUITE 300 CARMEL INDIANA 46032
Phone	3179893100
Name of Person for Whose Account the Securities are To Be Sold	Bartram Richard
See the definition of "person" in paragraph (a) of Rule 144. Information is to be given not only as to the person for whose account the securities are to be sold but also as to all other persons included in that definition. In addition, information shall be given as to sales by all persons whose sales are required by paragraph (e) of Rule 144 to be aggregated with sales for the account of the person filing this notice.
Relationship to Issuer	Former Officer

144: Securities Information

Title of the Class of Securities To Be Sold	Name and Address of the Broker	Number of Shares or Other Units To Be Sold	Aggregate Market Value	Number of Shares or Other Units Outstanding	Approximate Date of Sale	Name the Securities Exchange
Common	Fidelity Brokerage Services LLC 900 Salem Street Smithfield RI 02917	1061	30217.49	47510243	03/25/2026	NASDAQ

Furnish the following information with respect to the acquisition of the securities to be sold and with respect to the payment of all or any part of the purchase price or other consideration therefor:

144: Securities To Be Sold

Title of the Class	Date you Acquired	Nature of Acquisition Transaction	Name of Person from Whom Acquired	Is this a Gift?	Date Donor Acquired	Amount of Securities Acquired	Date of Payment	Nature of Payment *
Common	03/23/2026	Restricted Stock Vesting	Issuer			1061	03/23/2026	Compensation

* If the securities were purchased and full payment therefor was not made in cash at the time of purchase, explain in the table or in a note thereto the nature of the consideration given. If the consideration consisted of any note or other obligation, or if payment was made in installments describe the arrangement and state when the note or other obligation was discharged in full or the last installment paid.

Furnish the following information as to all securities of the issuer sold during the past 3 months by the person for whose account the securities are to be sold.

144: Securities Sold During The Past 3 Months

Name and Address of Seller	Title of Securities Sold	Date of Sale	Amount of Securities Sold	Gross Proceeds
Richard Bartram 11711 N. Meridian Street Suite 300 Carmel IN 46032	Common	03/16/2026	10000	300471.00

144: Remarks and Signature

Remarks	Sale includes an amount necessary to cover a tax obligation resulting from the settlement of a vested equity award distribution.
Date of Notice	03/25/2026
ATTENTION:
The person for whose account the securities to which this notice relates are to be sold hereby represents by signing this notice that he does not know any material adverse information in regard to the current and prospective operations of the Issuer of the securities to be sold which has not been publicly disclosed. If such person has adopted a written trading plan or given trading instructions to satisfy Rule 10b5-1 under the Exchange Act, by signing the form and indicating the date that the plan was adopted or the instruction given, that person makes such representation as of the plan adoption or instruction date.
Signature	/s/Wade Moss, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Richard B. Bartram
ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)