SCHEDULE: EcoR1 Capital Increases Zymeworks Stake to 30.7%

Activist investor EcoR1 Capital, LLC, and its affiliates, now beneficially own 30.7% of Zymeworks Inc. common stock, with an EcoR1 employee appointed Acting Chief Investment Officer.

Summary

• EcoR1 Capital, LLC, Oleg Nodelman, and EcoR1 Capital Fund Qualified, L.P. collectively reported beneficial ownership of 22,970,388 shares of Zymeworks Inc. Common Stock, representing 30.7% of the class.
• This percentage is calculated based on 74,836,534 shares outstanding as of November 4, 2025.
• EcoR1 Capital Fund Qualified, L.P. paid an aggregate of $192,880,935.01 for its Common Stock, including $47,364,999.62 for prefunded warrants exercised on June 26, 2025.
• EcoR1 Capital Fund, L.P. paid an aggregate of $12,853,702.36 for its Common Stock, including $2,634,993.17 for prefunded warrants exercised on June 26, 2025.
• Scott Platshon, an EcoR1 employee, resigned from Zymeworks' board of directors on November 16, 2025, and was concurrently appointed as the Issuer's Acting Chief Investment Officer.
• Oleg Nodelman, manager of EcoR1, remains a member of Zymeworks' board of directors.
• The reporting persons acquired the stock for investment purposes, believing it was undervalued and represented an attractive investment opportunity.
• They plan to routinely monitor Zymeworks and may take actions such as purchasing or selling additional shares, entering hedging transactions, or communicating with other stockholders and management.

Sentiment

Score: 7

Explanation: The sentiment is moderately positive due to a significant institutional investor increasing its stake, expressing belief in undervaluation, and placing a representative in a key management role, suggesting active engagement to unlock value.

Positives

• A significant institutional investor, EcoR1 Capital, holds a substantial 30.7% stake, indicating strong conviction in Zymeworks' value.
• The appointment of an EcoR1 employee, Scott Platshon, as Acting Chief Investment Officer suggests a deeper level of engagement and potential for strategic influence from a major shareholder.
• The reporting persons explicitly state their belief that Zymeworks' Common Stock was undervalued at the time of purchase, signaling potential upside.

Risks

• The reporting persons may engage in activist actions, which could lead to management changes, strategic shifts, or other events that may or may not align with all shareholder interests.
• Future actions by EcoR1, such as selling a portion or all of their holdings, could put downward pressure on the stock price.
• The investment thesis of undervaluation is subject to market conditions and Zymeworks' operational performance, which may not materialize as expected.

Future Outlook

The reporting persons intend to routinely monitor Zymeworks Inc. regarding various factors affecting their investment. They may purchase additional shares, sell existing holdings, engage in hedging transactions, and communicate with other stakeholders. While they have no present plans for specific corporate actions, they may recommend actions to Zymeworks' management, board, and stockholders, potentially including mergers, consolidations, asset sales, changes in control, or other capitalization changes.

Management Comments

• Oleg Nodelman, manager of EcoR1 Capital, LLC, signed the filing, affirming the information to be true, complete, and correct to the best of his knowledge and belief.

Industry Context

This filing indicates a significant activist investment in the biotechnology sector, where specialized funds like EcoR1 Capital often take large stakes in companies they believe are undervalued or mismanaged. Such substantial ownership can lead to increased shareholder influence on corporate strategy, R&D priorities, and capital allocation, potentially impacting the company's competitive position within the industry.

Management Changes

Corporate Governance

Related Party Transactions

• Oleg Nodelman serves as the manager and control person of EcoR1 Capital, LLC, and is also a member of Zymeworks Inc.'s board of directors.
• EcoR1 Capital, LLC is the investment adviser to investment funds, including EcoR1 Capital Fund Qualified, L.P., which holds a significant stake in Zymeworks Inc.
• Scott Platshon, an employee of EcoR1 Capital, was appointed as Zymeworks Inc.'s Acting Chief Investment Officer.

Stakeholder Impact

• Shareholders: Potential for increased shareholder value if EcoR1's investment thesis and strategic influence prove successful. Could also lead to volatility if EcoR1's actions are perceived negatively or if they alter their stake.
• Management: The appointment of an EcoR1 representative as Acting CIO could lead to shifts in internal investment strategy and decision-making.
• Employees: The new Acting CIO may bring changes to the company's investment team or strategy.

Next Steps

• EcoR1 Capital and its affiliates will routinely monitor Zymeworks Inc.'s operations, assets, prospects, financial position, and business development.
• They may purchase additional Common Stock or other securities of Zymeworks Inc. in the open market or through privately negotiated transactions.
• They may sell all or part of their Common Stock holdings at any time.
• They may enter into or unwind hedging or other derivative transactions with respect to the Common Stock.
• They may communicate with other stockholders, industry participants, and interested parties about Zymeworks Inc.
• They may recommend actions to Zymeworks' management, board of directors, and stockholders, potentially involving significant corporate events.

Key Dates

Keywords

Zymeworks Inc., EcoR1 Capital, Schedule 13D, Beneficial Ownership, Activist Investor, Biotechnology, Common Stock, Chief Investment Officer, Board of Directors, Investment Strategy