MBX affiliate reports multiple share sales

MBX reported Form 144 sales and related option information by an affiliate.

Rhea-AI Filing Summary

MBX reported Form 144 sales and related option information by an affiliate. The filing lists multiple open-market dispositions by Richard B. Bartram: 10,000 shares on 03/16/2026, 1,061 shares on 03/25/2026, 10,423 shares on 04/22/2026, 5,000 shares on 05/01/2026, 10,000 shares on 05/07/2026, and 10,000 shares on 05/08/2026, each with the cash proceeds shown in the filing. The notice also lists option grants that may underlie future sales (examples include 5,000 shares, 5,000 shares, 7,500 shares, and 5,000 shares tied to grant dates). This filing is a disclosure of recent dispositions and option-related holdings; it reports transactions rather than corporate actions.

Insights

Securities Counsel

Form 144 discloses multiple open-market sales and option grant listings by an affiliate.

The filing itemizes cash sales by Richard B. Bartram on specific dates with per-sale proceeds recorded (for example, 10,000 shares for $300,471 on 03/16/2026 and 10,000 shares for $379,562.50 on 05/08/2026). These entries fulfill Rule 144 notice requirements for restricted or control securities offered for sale.

Timing and magnitude of future sales depend on option exercises and any volume/holding limitations; subsequent filings or broker reports could show additional disposition activity. Cash‑flow treatment is the seller's proceeds as listed.

Key Figures

Sale on 03/16/2026: 10,000 shares Sale on 04/22/2026: 10,423 shares Sale on 05/08/2026: 10,000 shares +2 more

5 metrics

Sale on 03/16/2026 10,000 shares proceeds $300,471

Sale on 04/22/2026 10,423 shares proceeds $341,377.72

Sale on 05/08/2026 10,000 shares proceeds $379,562.50

Option grant example 7,500 shares Option Granted - 08/15/2023 (listed in filing)

Option grant example 5,000 shares Option Granted - 02/03/2025 (listed in filing)

Key Terms

Option Granted, Cash Common, Form 144

3 terms

Option Granted financial

"Common | 05/11/2026 | Option Granted - 04/20/2022"

Cash Common financial

"5000 | 05/11/2026 | Cash Common"

Form 144 regulatory

"144: Securities Sold During The Past 3 Months"

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.

FAQ

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

What does MBX Form 144 reveal about recent insider sales?

It lists specific dispositions by an affiliate: 10,000 shares on 03/16/2026, 1,061 on 03/25/2026, and additional dated sales. The filing shows per-sale cash proceeds tied to each transaction.

Who reported the shares sold in the MBX Form 144?

The filing identifies Richard B. Bartram as the reporting seller with an address in Carmel, IN. Multiple sale dates and share amounts are itemized in the notice.

Are there option grants shown in the MBX Form 144 filing?

Yes. The filing lists option-related entries including grants of 5,000; 5,000; 7,500; and 5,000 shares with grant dates ranging from 04/20/2022 to 02/03/2025 as presented.

Do the Form 144 entries state who received the cash proceeds?

The filing records cash proceeds per sale (for example, $300,471 for 10,000 shares on 03/16/2026), reflecting amounts received by the seller as shown in the notice.

Does this Form 144 itself change company governance or financials?

No. The form is a notice of securities offered for sale and lists transactions; it does not report corporate governance changes or company financial results.

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

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Accepted by SEC EDGAR 05/11/2026 - 03:54 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	22500	991901.00	47597536	05/11/2026	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	05/11/2026	Option Granted - 04/20/2022	Issuer			5000	05/11/2026	Cash
Common	05/11/2026	Option Granted - 11/07/2022	Issuer			5000	05/11/2026	Cash
Common	05/11/2026	Option Granted - 08/15/2023	Issuer			7500	05/11/2026	Cash
Common	05/11/2026	Option Granted - 02/03/2025	Issuer			5000	05/11/2026	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
Richard B. Bartram 11711 N. Meridian Street Suite 300 Carmel IN 48032	Common	05/08/2026	10000	379562.50

144: Remarks and Signature

Remarks
Date of Notice	05/11/2026
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/ Eric Janiak, 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)