Cullinan Therapeutics, Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

(Rule 14a-101)

Information Required in Proxy Statement

Schedule 14A Information

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

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Check the appropriate box:

(Name of Registrant as Specified in its Charter)

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April 28, 2026

Dear Cullinan Stockholder:

I am pleased to invite you to attend the 2026 Annual Meeting of Stockholders (the “Annual Meeting”) of Cullinan Therapeutics, Inc. (the “Company”). The meeting will be held online on June 16, 2026 at 10:00 a.m. Eastern Time. The Annual Meeting will be a virtual meeting in order to facilitate stockholder attendance and participation by enabling stockholders to participate from any location and at no cost to the stockholder. The meeting will be conducted via live webcast.

Details regarding admission to the Annual Meeting and the business to be conducted are more fully described in the accompanying Notice of Internet Availability of Proxy Materials (“Notice of Availability”) and proxy statement.

At the Annual Meeting, the agenda includes:

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the election of two (2) Class III directors, Nadim Ahmed and Stephen Webster, each for a three-year term until his successor has been duly elected and qualified, or until his earlier death, resignation or removal;

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the ratification of the appointment of KPMG LLP as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2026;

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the approval of an advisory vote on named executive officer compensation; and

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the transaction of any other business properly brought before the Annual Meeting or any adjournment or postponement of the Annual Meeting.

Under Securities and Exchange Commission rules, the Company is providing access to the proxy materials for the Annual Meeting to stockholders via the Internet. Accordingly, you can access the proxy materials and vote at www.proxyvote.com. Instructions for accessing the proxy materials and voting are described below and in the Notice of Availability that you received in the mail.

Your vote is very important. Whether or not you plan to virtually attend the Annual Meeting, please carefully review the enclosed proxy statement and then cast your vote, regardless of the number of shares you hold. If you are a stockholder of record, you may vote over the Internet, by telephone, by mail, or, if you request to receive a printed set of the proxy materials, by following the directions on the Notice of Availability. Submitting your vote via the Internet or by telephone or proxy card will not affect your right to vote during the meeting if you decide to virtually attend the Annual Meeting. If your shares are held in street name (held for your account by a broker or other nominee), you will receive instructions from your broker or other nominee explaining how to vote your shares, and you will have the option to cast your vote by telephone or over the Internet if the voting instruction form from your broker or nominee includes instructions and a toll-free telephone number or Internet website to do so. In any event, to be sure that your vote will be received in time, please cast your vote by your choice of available means at your earliest convenience.

We hope that you will join us on June 16, 2026. Your investment and continuing interest in the Company are very much appreciated.

Sincerely,

/s/ Nadim Ahmed

Nadim Ahmed

President and Chief Executive Officer

NOTICE OF 2026 ANNUAL MEETING OF STOCKHOLDERS

By order of the Board of Directors,

/s/ Jacquelyn Sumer

Jacquelyn Sumer

Corporate Secretary

Cambridge, Massachusetts

April 28, 2026

We first made these proxy materials available to stockholders on or about April 28, 2026. A copy of our Annual Report on Form 10-K for the fiscal year ended December 31, 2025, as filed with the Securities and Exchange Commission (the “SEC”), except for exhibits, will be furnished without charge to any stockholder upon written request to Cullinan Therapeutics, Inc., One Main Street, Suite 1350, Cambridge, Massachusetts 02142, Attention: Corporate Secretary. This proxy statement and our Annual Report on Form 10-K for the fiscal year ended December 31, 2025 are also available on the SEC’s website at www.sec.gov.

TABLE OF CONTENTS

One Main Street

Suite 1350

Cambridge, MA 02142