SCHEDULE: OrbiMed's Stake in MBX Biosciences Dips Below 10%

OrbiMed Advisors and its affiliates reported a decrease in their beneficial ownership of MBX Biosciences, Inc. common stock to 9.0% due to an increase in the issuer's outstanding shares.

Summary

• OrbiMed Advisors LLC, OrbiMed Capital GP VII LLC, and OrbiMed Genesis GP LLC (collectively, 'Reporting Persons') filed Amendment No. 1 to their Schedule 13D.
• The amendment reports a decrease in beneficial ownership of MBX Biosciences, Inc. common stock by more than 1%.
• This decrease is attributed to an increase in the number of outstanding shares of MBX Biosciences, Inc.
• As of the filing date, OrbiMed Advisors LLC beneficially owns 4,002,887 shares, representing 9.0% of the outstanding common stock.
• OrbiMed Capital GP VII LLC beneficially owns 3,255,000 shares, representing 7.3%.
• OrbiMed Genesis GP LLC beneficially owns 747,887 shares, representing 1.7%.
• The total outstanding shares used for calculation is 44,700,281, as reported in the Issuer's Rule 424(b)(5) Prospectus filed on September 25, 2025.
• The Reporting Persons retain certain registration rights, including Demand, Form S-3, and Piggyback registration rights, under an Investors' Rights Agreement dated August 2, 2204.

Sentiment

Score: 5

Explanation: This filing is a routine disclosure of a change in beneficial ownership percentage due to share dilution, not a reflection of company performance or a strategic move by the investor. It is a neutral, factual update.

Positives

• Reporting Persons retain significant registration rights (Demand, Form S-3, Piggyback) which provide flexibility for future share dispositions.

Negatives

• Beneficial ownership percentage decreased by more than 1% due to an increase in the issuer's outstanding shares, diluting the Reporting Persons' stake.

Risks

• Reporting Persons may dispose of some or all of their currently owned shares in the open market or privately negotiated transactions, which could exert downward pressure on the stock price.

Future Outlook

Reporting Persons intend to review their investment based on various factors and may acquire or dispose of shares. They have not formulated plans for extraordinary corporate transactions, management changes, or material changes to the Issuer's business or corporate structure at this time.

Management Comments

• No direct quotes or paraphrased statements from MBX Biosciences, Inc. management are included in this filing, as it is filed by the Reporting Persons (OrbiMed).

Industry Context

Not applicable as this filing primarily concerns an investor's beneficial ownership stake and does not provide sufficient information on the issuer's industry context.

Comparison to Industry Standards

• Not applicable, as this filing focuses on changes in beneficial ownership by an investment group and does not contain performance metrics or operational details for comparison.

Corporate Governance

Stakeholder Impact

• Shareholders: Potential for increased liquidity if Reporting Persons exercise registration rights and sell shares; potential for dilution if new shares were issued.
• Company (MBX Biosciences): The increase in outstanding shares likely provided capital, but the decrease in a major investor's percentage stake could be noted.

Next Steps

• Reporting Persons will continue to review their investment in MBX Biosciences, Inc. based on various factors.
• Reporting Persons may acquire additional shares or other securities of the Issuer in the open market or privately negotiated transactions.
• Reporting Persons may dispose of some or all of their currently owned shares in the open market or privately negotiated transactions.

Key Dates

Recommendation

This filing is a routine disclosure of a decrease in beneficial ownership percentage by OrbiMed due to an increase in MBX Biosciences' outstanding shares, which was likely already known through the prospectus. It does not provide new information regarding the company's operational performance or a definitive change in OrbiMed's long-term investment strategy beyond a general statement of intent to review their position. Therefore, a 'hold' recommendation is appropriate as there's no strong catalyst for a buy or sell decision based solely on this filing.

Keywords

MBX Biosciences, OrbiMed Advisors, Schedule 13D, Beneficial Ownership, Common Stock, Investment, Registration Rights, Equity Stake