SCHEDULE: Adage Capital Takes 6.13% Stake in 89bio Amid Roche Merger

Adage Capital Management, L.P. and its principals have disclosed a 6.13% beneficial ownership stake in 89bio, Inc., acquired for investment purposes in anticipation of the company's merger with Roche Holdings, Inc.

Summary

• Adage Capital Management, L.P., Robert Atchinson, and Phillip Gross (the "Reporting Persons") have reported beneficial ownership of 9,097,587 shares of 89bio, Inc. Common Stock.
• This stake represents 6.13% of 89bio, Inc.'s outstanding Common Stock, calculated based on 148,492,428 shares outstanding as of September 16, 2025.
• The shares were acquired for approximately $125,505,893, inclusive of commissions, from the working capital of Adage Capital Partners, L.P.
• The acquisition was made for investment purposes, specifically employing merger arbitrage and event-driven strategies, as the Reporting Persons believed the shares represented an attractive investment opportunity.
• 89bio, Inc. previously announced on September 18, 2025, that it entered into a Merger Agreement with Roche Holdings, Inc. and Bluefin Merger Subsidiary, Inc. on September 17, 2025.
• Adage Capital Management, L.P. (ACM) previously consented to an SEC Order on September 25, 2024, for late filings under Sections 13(d) and 16(a) of the Act in 2020 and 2021, resulting in a civil money penalty of $200,000.
• ACM has since implemented additional policies and procedures to prevent future inadvertent Section 13 and Section 16 violations.

Sentiment

Score: 7

Explanation: The filing indicates a strategic investment by a sophisticated firm, Adage Capital, in 89bio, Inc., driven by an attractive investment opportunity related to a pending merger with Roche. While Adage Capital Management had a past SEC violation, they have taken remedial actions. The overall sentiment is neutral to slightly positive, reflecting a strategic investment in a company undergoing a significant corporate event.

Positives

• Reporting Persons acquired the shares because they believed they represented an attractive investment opportunity.
• Adage Capital Management, L.P. has implemented additional policies and procedures to prevent future inadvertent Section 13 and Section 16 violations following a past SEC Order.
• Adage Capital Management, L.P. undertook remedial acts and cooperated with SEC staff regarding past violations.

Negatives

• Adage Capital Management, L.P. (ACM) was subject to an SEC Order on September 25, 2024, for violations (late filings) of Sections 13(d) and 16(a) of the Securities Exchange Act in 2020 and 2021.
• ACM paid a civil money penalty of $200,000 as part of the SEC Order.

Risks

• The Reporting Persons may not be eligible to report their position on a Schedule 13G due to their investment strategies, including merger arbitrage and event-driven strategies.
• Future actions regarding the investment are subject to various factors, including the terms of the Proposed Transaction, other offers, the Issuer's financial position and strategic direction, actions by the Board of Directors, stock price levels, other investment opportunities, and general market conditions.

Future Outlook

The Reporting Persons intend to continuously review their investment in 89bio, Inc. and may engage in discussions with management, the Board of Directors, and other shareholders. Depending on various factors, including the terms of the Proposed Transaction, market conditions, and the Issuer's strategic direction, they may purchase additional shares, sell existing shares, engage in short selling or hedging, or otherwise change their investment intentions.

Management Comments

• "The Reporting Persons acquired the shares of Common Stock to which this Schedule 13D relates for investment purposes in the ordinary course of business, and not with the purpose nor with the effect of changing or influencing the control or management of the Issuer."
• "The Reporting Persons acquired the shares of Common Stock pursuant to investment strategies, including merger arbitrage and event driven strategies, because they believed that the shares of Common Stock reported herein, when purchased, represented an attractive investment opportunity."

Industry Context

This filing highlights a significant investment by a prominent hedge fund, Adage Capital, in a biotechnology company, 89bio, Inc., specifically leveraging a merger arbitrage strategy following 89bio's announced acquisition by Roche Holdings, Inc. This activity reflects broader trends in the biotechnology and pharmaceutical sectors, where strategic acquisitions and consolidation are common, often attracting event-driven investment strategies.

Comparison to Industry Standards

• NA

Corporate Governance

Legal Proceedings

• Adage Capital Management, L.P. consented to an Order Instituting Cease-And-Desist Proceedings by the SEC on September 25, 2024, for late filings under Sections 13(d) and 16(a) of the Act in 2020 and 2021, resulting in a $200,000 civil money penalty.

Related Party Transactions

• A Joint Filing Agreement was executed among Adage Capital Management, L.P., Robert Atchinson, and Phillip Gross for the purpose of filing this Schedule 13D.

Stakeholder Impact

• Shareholders of 89bio, Inc.: The significant investment by Adage Capital, a prominent institutional investor, signals confidence in the company's valuation, particularly in the context of the pending merger with Roche Holdings, Inc. This could positively influence market perception and trading activity.
• Roche Holdings, Inc.: The investment by Adage Capital, employing a merger arbitrage strategy, indicates market participants are actively positioning themselves around the announced acquisition, potentially affecting the arbitrage spread.

Next Steps

• Reporting Persons will review their investment in 89bio, Inc. on a continuing basis.
• Reporting Persons may engage in discussions with 89bio management, Board of Directors, other shareholders, and relevant parties concerning their investment.
• Reporting Persons may purchase additional shares, sell some or all of their shares, engage in short selling or hedging transactions, and/or change their investment intentions based on various factors.

Key Dates

Recommendation

The filing details a significant investment by Adage Capital, an experienced firm, in 89bio, Inc. with an explicit merger arbitrage strategy related to the announced acquisition by Roche Holdings. For existing shareholders, holding until the merger's completion or selling into any premium created by the arbitrage activity is a common strategy. For new investors, entering an arbitrage play requires careful consideration of the merger terms, completion risk, and spread, making a general 'buy' recommendation inappropriate without further specific analysis of the merger terms and market conditions.

Keywords

89bio Inc., Adage Capital Management, Roche Holdings, Merger Agreement, Schedule 13D, Beneficial Ownership, Merger Arbitrage, Biotechnology, Investment Stake, SEC Filing