Zenas BioPharma, Inc.

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PROXY STATEMENT SUMMARY

This Proxy Statement relates to the solicitation of proxies by the board of directors (the “board of directors”) of Zenas BioPharma, Inc. for use at its 2025 Annual Meeting of Stockholders (the “Annual Meeting”) to be held in a virtual format atwww.virtualshareholdermeeting.com/ZBIO2025 on June 10, 2025 at 8:00 a.m. Eastern Time, or at any other time following adjournment or postponement thereof. You are invited to participate in the Annual Meeting and to vote on the proposals described in this proxy statement (the “Proxy Statement”).

What Proposals Will Be Voted On At the Annual Meeting?

The proposals to be voted on at the Annual Meeting are as follows:

To elect the two Class I director nominees named in the Proxy Statement to serve until the 2028 Annual Meeting of Stockholders and until their successors are duly elected and qualified

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To ratify the appointment of Ernst & Young LLP as the Company’s independent registered public accounting firm for the year ending December 31, 2025

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We will also consider any other matters that may properly come before the Annual Meeting or any adjournments or postponements thereof.

How Does the Board of Directors Recommend That I Vote?

The board of directors recommends that you vote your shares “FOR” each director nominee in Proposal 1 and “FOR” Proposal 2.

Who Can Vote?

Only stockholders of record at the close of business on April 14, 2025 (the “Record Date”) are entitled to notice of the Annual Meeting and to vote on the proposals described in this Proxy Statement. At the close of business on the Record Date, 41,834,182 shares of our common stock were issued and outstanding. We will make available a list of stockholders of record as of the Record Date for inspection by stockholders for any purpose germane to the Annual Meeting during the ten days preceding the Annual Meeting. To access the stockholder list during this time, please send your request, and proof of ownership, to our corporate secretary via e-mail at legalnotices@zenasbio.com.

How Can I Participate in the Virtual Annual Meeting?

Stockholders of record as of the close of business on the Record Date are entitled to participate in and vote at the Annual Meeting. To participate in the Annual Meeting, including to vote and ask questions, stockholders of record should go to the meeting website atwww.virtualshareholdermeeting.com/ZBIO2025, enter the 16-digit control number found on your proxy card or Notice, and follow the instructions on the website. If your shares are held in street name and your voting instruction form or Notice indicates that you may vote those shares throughwww.proxyvote.com, then you may access, participate in and vote at the Annual Meeting with the 16-digit access code indicated on that voting instruction form or Notice. Otherwise, stockholders who hold their shares in street name and wish to attend, participate in or vote at the Annual Meeting should contact their bank, broker or other nominee (preferably at least five days before the Annual Meeting) and obtain a “legal proxy” in order to be able to attend, participate in or vote at the Annual Meeting. Stockholders who hold their shares in street name may vote in advance by providing voting instructions to their bank, broker or other nominee in advance of the meeting (see “How Do I Vote?” below).

We will endeavor to answer as many stockholder-submitted questions as time permits that comply with the Annual Meeting rules of conduct. We reserve the right to edit profanity or other inappropriate language and to exclude questions regarding topics that are not pertinent to meeting matters or Company business being conducted at the Annual Meeting. If we receive substantially similar questions, we may group such questions together and provide a single response to avoid repetition.

The meeting webcast will begin promptly at 8:00 a.m. Eastern Time. Online check-in will begin approximately 15 minutes before then, and we encourage you to allow ample time for check-in procedures.

If you experience technical difficulties during the check-in process or during the meeting, please call the number listed on the meeting website for technical support. Additional information regarding the rules and procedures for participating in the Annual Meeting will be set forth in our meeting rules of conduct, which stockholders can view during the meeting at the meeting website.

Why Are We Holding a Virtual Annual Meeting?

We have adopted a virtual meeting format for the Annual Meeting to provide a consistent experience to all stockholders regardless of geographic location. We believe this expands stockholder access, improves communications and lowers our costs while reducing the environmental impact of the meeting. In structuring our virtual Annual Meeting, our goal is to enhance rather than constrain stockholder participation in the meeting, and we have designed the meeting to provide stockholders with the same rights and opportunities to participate as they would have at an in-person meeting.

Why Did I Receive a Notice of Internet Availability?

Pursuant to SEC rules, we are furnishing the proxy materials to our stockholders primarily via the Internet instead of mailing printed copies. This process allows us to expedite our stockholders’ receipt of proxy materials, lower the costs of printing and mailing the proxy materials and reduce the environmental impact of our Annual Meeting. The Notice provides instructions on how to access the proxy materials for the Annual Meeting via the Internet, how to request a printed set of proxy materials and how to vote your shares. You will not receive a printed copy of the proxy materials unless you request one.

What Is the Difference between Holding Shares as a Registered Stockholder and as a Beneficial Owner?

If your shares of common stock are registered directly in your name with our transfer agent, Computershare Trust Company, N.A., you are considered to be, with respect to those shares of common stock, the registered stockholder, and these proxy materials are being sent directly to you by us.

If your shares of common stock are held by a broker, bank or other nominee, you are considered the beneficial owner of shares of common stock held in “street name,” and these proxy materials are being forwarded to you from that broker, bank or other nominee.

How Do I Vote?

Even if you plan to attend the Annual Meeting, we recommend that you also submit your vote as early as possible in advance so that your vote will be counted if you later decide not to, or are unable to, virtually attend the Annual Meeting.

If you are the registered stockholder, you may vote your shares online during the virtual Annual Meeting (see “How Can I Participate in the Virtual Annual Meeting?” above) or by proxy in advance of the Annual Meeting by Internet (atwww.proxyvote.com) or, if you requested paper copies of the proxy materials, by completing and mailing a proxy card or by telephone (at 800-690-6903).

If you are the beneficial owner, you are not a record owner, and you therefore have no direct vote on any matter to come before the Annual Meeting. Your broker, bank or nominee will send you voting instructions for you to use in directing the broker, bank or nominee in how to vote your shares. Your broker, bank or nominee may allow you to deliver your voting instructions via the telephone or the Internet. You also may vote your shares online during the virtual Annual Meeting if you obtain a “legal proxy” from your broker, bank or nominee (see “How Can I Participate in the Virtual Annual Meeting?” above).

What Happens If I Do Not Vote?

If you are the registered stockholder and do not vote in one of the ways described above, your shares will not be voted at the Annual Meeting and will not be counted toward the quorum requirement.

A “broker non-vote” occurs when a broker, bank or other nominee holding shares for a beneficial owner does not vote the shares on a proposal because the broker, bank or other nominee does not have discretionary voting power for a particular item and has not received instructions from the beneficial owner regarding voting. Brokers, banks or other nominees who hold shares for the accounts of their clients have discretionary authority to vote shares if specific instructions are not given with respect to “routine” matters. Although the determination of whether a matter is “routine” is typically determined only after proxy materials are filed with the SEC, we expect that the proposal on ratification of the appointment of our independent registered public accounting firm (Proposal 2) will be a “routine” matter and that the election of each nominee for director (Proposal 1), will be a “non-routine” matter. Accordingly, if you hold your shares through a broker, bank or other nominee and you do not timely provide your broker, bank or other nominee with specific instructions on how to vote your shares, your broker, bank or other nominee would not be authorized to cast a vote on your behalf on Proposal 1 (election of each nominee for director), but would be authorized to cast a vote on your behalf, in its discretion, on Proposal 2 (ratification of the appointment of Ernst & Young LLP). In such cases, a “broker non-vote” may be entered with respect to your shares on Proposal 1 to reflect that your broker was present with respect to your shares at the meeting but was not exercising voting rights on your behalf with respect to those shares. Brokers, banks and other nominees generally have discretionary authority to vote on the ratification of the appointment of an independent registered public accounting firm (Proposal 2); thus, we do not expect any broker non-votes on this matter. Broker non-votes and abstentions will have no effect on the outcome of each proposal.

What If I Sign and Return a Proxy Card or Otherwise Vote but Do Not Indicate Specific Choices?

The shares represented by each signed and returned proxy will be voted at the Annual Meeting by the persons named as proxies in the proxy card in accordance with the instructions indicated on the proxy card. However, if you are the registered stockholder and sign and return your proxy card without giving specific instructions, the persons named as proxies in the proxy card will vote your shares in accordance with the recommendations of the board of directors. Your shares will be counted toward the quorum requirement.

If you are the beneficial owner and do not direct your broker, bank or other nominee how to vote your shares, your broker, bank or other nominee may vote your shares with respect to proposals considered to be “routine.” Your broker, bank or other nominee is not entitled to vote your shares with respect to “non-routine” proposals. Accordingly, if you hold your shares through a broker, bank or other nominee and you do not timely provide your broker, bank or other nominee with specific instructions on how to vote your shares, your broker, bank or other nominee would not be authorized to cast a vote on your behalf on Proposal 1 (election of each nominee for director), but would be authorized to cast a vote on your behalf, in its discretion, on Proposal 2 (ratification of the appointment of Ernst & Young LLP) (see “What Happens If I Do Not Vote?” above).

Can I Change My Vote after I Submit My Proxy?

If you are the registered stockholder, you may revoke your proxy at any time before the final vote at the Annual Meeting in any one of the following ways:

You may complete and submit a new proxy card, but it must bear a later date than the original proxy card;

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You may submit new proxy instructions via telephone or the Internet;

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You may send a timely written notice that you are revoking your proxy to our Corporate Secretary at the address set forth on the first page of this Proxy Statement; or

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You may vote by attending the Annual Meeting virtually. However, your virtual attendance at the Annual Meeting will not, by itself, revoke your proxy.

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Your last submitted vote is the one that will be counted.

If you are the beneficial owner, you must follow the instructions you receive from your broker, bank or other nominee with respect to changing your vote.

What Is the Quorum Requirement?

The holders of a majority of the shares of common stock outstanding and entitled to vote at the Annual Meeting must be present, either virtually or represented by proxy, at the Annual Meeting to constitute a quorum. A quorum is required to transact business at the Annual Meeting.

Your shares will be counted toward the quorum only if you submit a valid proxy (or a valid proxy is submitted on your behalf by your broker, bank or other nominee) or if you attend the Annual Meeting virtually and vote. Abstentions and broker non-votes, if any, will be counted toward the quorum requirement. If there is no quorum, the chair of the Annual Meeting may adjourn the Annual Meeting to another time or date.

How Many Votes Are Required to Approve Each Proposal and How Are Votes Counted?

Votes will be counted by Broadridge Financial Solutions, the Inspector of Elections appointed for the Annual Meeting.

Proposal 1: Election of Directors

A majority of the votes properly cast for election of a director will effect such election. However, in the event that stockholders are to select among several alternative nominees in an election of directors (such as when there are more nominees than directorships), directors will be elected from among the nominees based on those directors receiving the most “for” votes until all board seats are filled. A properly returned proxy indicating “abstain” with respect to the election of one or more directors will not be counted as a vote cast with respect to the director or directors indicated. Broker non-votes will not be counted as votes cast on the proposal and will have no effect on the election of directors.

Proposal 2: Ratification of Appointment of Independent Registered Public Accounting Firm

A majority of votes properly cast will approve the proposal to ratify the appointment of Ernst & Young LLP as our independent registered public accounting firm. Abstentions and broker non-votes, if any, will have no effect on the outcome of the matter. Please note, however, that because the vote on the ratification of Ernst & Young LLP is advisory in nature, the results of such vote will not be binding upon the board of directors or its committees.

What If Another Matter Is Properly Brought before the Annual Meeting?

As of the date of filing this Proxy Statement, the board of directors knows of no other matters that will be presented for consideration at the Annual Meeting. If any other matters are properly brought before the Annual Meeting, it is the intention of the persons named as proxies in the proxy card to vote on such matters in accordance with their best judgment.

How Many Votes Do I Have?

Each share of common stock is entitled to one vote on each proposal to be voted on at the Annual Meeting.

What Does It Mean If I Receive More Than One Set of Proxy Materials?

If you receive more than one set of proxy materials, your shares may be registered in more than one name or held in different accounts. Please cast your vote with respect to each set of proxy materials that you receive to ensure that all of your shares are voted.

Who Is Paying for This Proxy Solicitation?

We are soliciting proxies from stockholders on behalf of our board of directors and we will pay the costs associated with the solicitation of proxies, including the preparation, assembly, printing and mailing of the proxy materials. We may also reimburse brokers, banks or other nominees for the cost of forwarding proxy materials to beneficial owners of shares of common stock held in “street name.”

Our employees, officers and directors may solicit proxies in person or via telephone or the Internet. We will not pay additional compensation for any of these services.

Additionally, we may retain proxy solicitation firms to encourage greater stockholder participation if the Company deems it necessary or desirable to do so. The costs of solicitation, which are not determinable at present, but in any event are not material to the Company, will also be borne by the Company.

How Can I Find out the Voting Results?

We expect to announce preliminary voting results at the Annual Meeting. Final voting results will be published in a Current Report on Form 8-K to be filed with the SEC within four business days after the Annual Meeting.