Zymeworks Inc.

Why am I receiving these materials?

Our board of directors (“Board of Directors”) is furnishing these materials in connection with our virtual Meeting to be held on December 30, 2025. This proxy statement is furnished in connection with the solicitation of proxies by or on behalf of management and the Board of Directors. This proxy statement is designed to assist you in voting your securities and includes information that we are required to provide under the rules of the U.S. Securities and Exchange Commission (the “SEC”).

The Notice of Internet Availability of Proxy Materials (the “Notice of Internet Availability”) containing instructions on how to access this proxy statement, the accompanying notice of annual meeting and form of proxy, and our annual report, is first being sent or given on or about November 18, 2025 to all stockholders and holders of exchangeable shares of record as of the close of business on November 3, 2025 (the “Record Date”). The proxy materials and our annual report can be accessed as of November 10, 2025 by visiting https://www.envisionreports.com/ZYME. If you receive a Notice of Internet Availability, then you will not receive a printed copy of the proxy materials or our annual report in the mail unless you specifically request these materials. Instructions for requesting a printed copy of the proxy materials and our annual report are set forth in the Notice of Internet Availability.

Why did I receive a Notice of Internet Availability instead of a full set of proxy materials?

In accordance with the rules of the SEC, we have elected to furnish our proxy materials, including this proxy statement and our annual report, primarily via the Internet. As a result, we are mailing to our stockholders and holders of exchangeable shares a Notice of Internet Availability instead of a paper copy of the proxy materials. The Notice of Internet Availability contains instructions on how to access our proxy materials on the Internet, how to vote on the proposals, how to request printed copies of the proxy materials and our annual report, and how to request to receive all future proxy materials in printed form by mail or electronically bye-mail. We encourage stockholders and holders of exchangeable shares to take advantage of the availability of the proxy materials on the Internet to help reduce our costs and the environmental impact of our annual meetings.

What does it mean if I receive more than one Notice of Internet Availability?

If you receive more than one Notice of Internet Availability, then your shares may be registered in more than one name and/or are registered in different accounts. Please follow the voting instructions on each Notice of Internet Availability to ensure that all of your shares are voted.

I share an address with another stockholder, and we received only one paper copy of the Notice of Internet Availability or proxy statement and annual report, as applicable. How may I obtain an additional copy of the Notice of Internet Availability or proxy statement and annual report, as applicable?

We have adopted a procedure approved by the SEC called “householding,” under which we can deliver a single copy of the Notice of Internet Availability and, if applicable, the proxy statement and annual report, to multiple stockholders who share the same address unless we receive contrary instructions from one or more stockholders. This procedure reduces our printing and mailing costs. Stockholders who participate in householding will continue to be able to access and receive separate proxy cards. Upon a written or oral request, we will promptly deliver a separate copy of the Notice of Internet Availability and, if applicable, the proxy statement and annual report, to any stockholder at a shared address to which we delivered a single copy of these documents. To receive a separate copy, or, if you are receiving multiple copies, to request that we only send a single copy of next year’s Notice of Internet Availability or proxy statement and annual report, as applicable, you may contact us as follows:

Attn: Corporate Secretary

legal@zymeworks.com

If you are a beneficial owner of shares and you wish to receive a separate set of proxy materials in the future, or if you have received multiple sets of proxy materials and would like to receive only one set in the future, please contact your bank or broker directly.

Who pays the cost of soliciting proxies for the Meeting?

We will bear the cost of solicitation. This solicitation of proxies is being made to stockholders and holders of exchangeable shares by mail, but may be supplemented by telephone or other personal contact. We have engaged Kingsdale Advisors (“Kingsdale”) as proxy solicitation agent and will pay fees of approximately $79,860 Canadian dollars to Kingsdale for the proxy solicitation service in addition to certainout-of-pocket expenses. That firm expects that approximately 30 of its employees will assist in the solicitation. We have retained Kingsdale to provide a broad array of strategic advisory, governance, strategic communications, digital and investor campaign services on a global retainer basis in addition to certain fees accrued during the life of the engagement upon the discretion and direction of Zymeworks.

We will reimburse brokerage houses and other custodians, nominees and fiduciaries for forwarding proxy materials to beneficial stockholders and beneficial holders of exchangeable shares.

What items of business will be voted on at the Meeting?

The business items to be voted on at the Meeting are:

What are my voting choices?

You may vote:

How does the Board of Directors recommend that I vote?

Our Board of Directors recommends that you vote your shares:

What vote is required to approve each item?

To conduct business at the Meeting, a quorum consisting of at least 33 1/3% of the voting power of our capital stock issued and outstanding and entitled to vote must be present in person (virtually) or represented by proxy. Exchangeable shares will only count towards the quorum if they have been voted or if the holder of the exchangeable shares is represented by a proxy holder at the Meeting.

As described below, brokernon-votes and abstentions will be counted for determining the presence or absence of a quorum for the transaction of business at the Meeting, but will not be considered votes cast for or against a proposal.

What happens if additional items are presented at the Meeting?

We are not aware of any item that may be voted on at the Meeting that is not described in this proxy statement. However, if any other matters are properly brought before the Meeting, the persons named as proxies will be authorized to vote or otherwise act on those matters in accordance with their judgment.

Where can I find the voting results?

We expect to announce preliminary voting results at the Meeting and to publish final results in a Current Report on Form 8-K that will be available on the SEC’s website atwww.sec.govand on the System for Electronic Document Analysis and Retrieval (“SEDAR+”) atwww.sedarplus.compromptly following the Meeting. The Current Report on Form 8-K will also be available on our website atwww.zymeworks.com.