Adicet Bio, Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No. )

Check the appropriate box:

☐ Preliminary Proxy Statement

☐Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

☒ Definitive Proxy Statement

☐ Definitive Additional Materials

☐ Soliciting Material under §240.14a-12

Adicet Bio, Inc.

(Name of Registrant as Specified in its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check all boxes that apply):

131 Dartmouth Street, 3rd Floor

Boston, Massachusetts 02116

NOTICE OF SPECIAL MEETING OF STOCKHOLDERS

To be held on December 19, 2025

Notice is hereby given that the Special Meeting of Stockholders (Special Meeting) of Adicet Bio, Inc., will be held online on December 19, 2025 at 8:00 a.m. Eastern Time. You may attend the meeting virtually via the Internet atwww.virtualshareholdermeeting.com/ACET2025SM, where you will be able to vote electronically and submit questions. You will need the 16-digit control number included with the proxy materials being mailed to you separately in order to attend the Special Meeting.

The purpose of the Special Meeting is the following:

To approve an amendment to our Restated Certificate of Incorporation (Certificate of Incorporation) to combine outstanding shares of our common stock, par value $0.0001 per share (Common Stock), into a lesser number of outstanding shares (the Reverse Stock Split), by a ratio of not less than one-for-five and not more than one-for-thirty, with the exact ratio to be set within this range by our board of directors (the Board) in its sole discretion (the Reverse Stock Split Proposal or Proposal No. 1).

To approve an adjournment of the Special Meeting, if necessary, to permit further solicitation and vote of proxies in the event that there are insufficient votes in favor of Proposal No. 1 (the Adjournment Proposal or Proposal No. 2).

Only Adicet Bio, Inc. stockholders of record at the close of business on November 14, 2025, will be entitled to vote at the Special Meeting and any adjournment or postponement thereof.

We are mailing to our stockholders this proxy statement and the accompanying proxy card (Proxy Materials). We plan to mail the Proxy Materials on or about November 17, 2025, which will contain instructions on how to access those documents and to cast your vote via the Internet.

To be admitted to the Special Meeting and vote your shares, you must provide the 16-digit control number as provided described in the proxy card or voting instruction form atwww.proxyvote.com. Please see the “General Information” section of the proxy statement that accompanies this notice for more details regarding the logistics of the virtual Special Meeting, including the ability of stockholders to submit questions during the Special Meeting, and technical details and support related to accessing the virtual platform.

Your vote is important. Whether or not you are able to attend the meeting in person, it is important that your shares be represented. To ensure that your vote is recorded promptly, please vote as soon as possible, even if you plan to attend the meeting, by submitting your proxy via the Internet at the address listed on the proxy card or by signing, dating, and returning the proxy card. If your shares are held in "street name," that is, held for your account by a broker or other nominee, you will receive instructions from the holder of record that you must follow for your shares to be voted.

By order of the board of directors,

/s/ Chen Schor

Chen Schor

President, Chief Executive Officer

Boston, Massachusetts

November 17, 2025

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