MBX Form 144: Proposed 10,000-Share Sale Listed

MBX reporting proposed sales of common stock under Form 144, listing multiple option-originated share lots and recent open-market dispositions.

Rhea-AI Filing Summary

MBX reporting proposed sales of common stock under Form 144, listing multiple option-originated share lots and recent open-market dispositions. The filing lists proposed sales of 10,000 shares through Fidelity Brokerage Services and shows prior sales totaling several reported transactions between 03/16/2026 and 05/07/2026.

The excerpt names three option grants with 2,500, 2,500, and 5,000 shares tied to grant dates and indicates cash settlement method for the listed option exercises.

Insights

Compliance Analyst

Form 144 lists proposed insider sales and recent dispositions; disclosure-focused, not an execution confirmation.

The filing lists proposed sales to be effected through Fidelity Brokerage Services and records prior completed sales on specific dates with exact share counts and proceeds. This is a regulatory notice required before public sale by affiliates.

Cash‑flow treatment for the listed option transactions is shown as Cash. Subsequent public filings will show whether the proposed sales were executed.

Key Figures

Proposed sale (broker listed): 10,000 shares Option lot 1: 2,500 shares Option lot 2: 2,500 shares +3 more

6 metrics

Proposed sale (broker listed) 10,000 shares Fidelity Brokerage Services LLC; <date>05/08/2026</date>; NASDAQ

Option lot 1 2,500 shares Option Granted - <date>04/20/2022</date>; settlement: Cash

Option lot 2 2,500 shares Option Granted - <date>11/07/2022</date>; settlement: Cash

Option lot 3 5,000 shares Option Granted - <date>08/15/2023</date>; settlement: Cash

Recent sale example 10,423 shares Sale on <date>04/22/2026</date>; proceeds listed as $341,377.72

Recent sale example 10,000 shares Sale on <date>03/16/2026</date>; proceeds listed as $300,471.00

Key Terms

Form 144, Option Granted, Securities Sold During The Past 3 Months, Cash

4 terms

Form 144 regulatory

"144: Securities To Be Sold"

Form 144 is a document that investors must file with the government when they plan to sell a large number of shares of a company's stock. It helps ensure transparency so everyone knows how many shares are being sold and when, which can impact the stock's price.

Option Granted financial

"Option Granted - 04/20/2022"

Securities Sold During The Past 3 Months regulatory

"144: Securities Sold During The Past 3 Months"

Cash financial

"05/08/2026 | Cash Common"

FAQ

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

What does MBX's Form 144 report about planned share sales?

The filing reports proposed sales of common stock, including a 10,000-share block through Fidelity Brokerage Services. It lists option-originated lots and identifies the settlement method as Cash for those option shares.

How many option-derived shares does MBX list as proposed to be sold?

The excerpt lists option-originated lots of 2,500, 2,500, and 5,000 shares tied to grant dates in 2022 and 2023. Each lot is described with its grant date and cash settlement method.

What recent insider sales does the MBX excerpt disclose?

Prior sales shown include transactions on 03/16/2026, 03/25/2026, 04/22/2026, 05/01/2026, and 05/07/2026, with share counts of 10,000, 1,061, 10,423, 5,000, and 10,000 respectively.

Who is the broker listed for MBX's proposed 10,000-share sale?

The broker named is Fidelity Brokerage Services LLC at 900 Salem Street, Smithfield, RI. The broker entry is associated with a 10,000-share proposed sale on 05/08/2026 to be traded on NASDAQ.

Does the Form 144 confirm sales were completed for the proposed lots?

No. Form 144 is a notice of proposed sale; it lists planned transactions and prior completed sales but does not by itself confirm that the newly proposed sales were executed.

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

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Accepted by SEC EDGAR 05/08/2026 - 12:21 PM Learn about SEC filing dates

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	10000	379562.50	47597536	05/08/2026	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	05/08/2026	Option Granted - 04/20/2022	Issuer			2500	05/08/2026	Cash
Common	05/08/2026	Option Granted - 11/07/2022	Issuer			2500	05/08/2026	Cash
Common	05/08/2026	Option Granted - 08/15/2023	Issuer			5000	05/08/2026	Cash

* 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 B. Bartram 11711 N. Meridian Street, Suite 300 Carmel IN 46032	Common	03/16/2026	10000	300471.00
Richard B. Bartram 11711 N. Meridian Street, Suite 300 Carmel IN 48032	Common	03/25/2026	1061	30217.49
Richard B. Bartram 11711 N. Meridian Street, Suite 300 Carmel IN 48032	Common	04/22/2026	10423	341377.72
Richard B. Bartram 11711 N. Meridian Street, Suite 300 Carmel IN 48032	Common	05/01/2026	5000	159000.00
Richard B. Bartram 11711 N. Meridian Street Suite 300 Carmel IN 48032	Common	05/07/2026	10000	322050.00

144: Remarks and Signature

Remarks
Date of Notice	05/08/2026
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)