Definium Therapeutics, Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

(RULE 14a-101)

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No. )

Filed by the Registrant ☒

Filed by a Party other than the Registrant ☐

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

Definium Therapeutics, 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):

☒ No fee required.

☐ Fee paid previously with preliminary materials.

☐ Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11.

One World Trade Center, Suite 8500

New York, New York 10007

(212) 220-6633

NOTICE OF ANNUAL GENERAL AND SPECIAL MEETING OF SHAREHOLDERS

To be held on June 11, 2026 at 10:00 a.m. Eastern Time.

Dear Shareholder:

You are cordially invited to attend the Annual General and Special Meeting of Shareholders (the “Annual Meeting”) of Definium Therapeutics, Inc. (the “Company” or “Definium”), a British Columbia company. All shareholders are invited to attend the Annual Meeting, which will be held virtually via live webcast at www.virtualshareholdermeeting.com/DFTX2026 on June 11, 2026 at 10:00 a.m. Eastern Time. To participate, vote or submit questions during the Annual Meeting, shareholders or their proxyholders must log on to the virtual meeting platform by entering the 16-digit control number included on your proxy card, Notice of Internet Availability of Proxy Materials (“Notice”) or voting instruction form. Online access to the Annual Meeting will open approximately 15 minutes prior to the start of the virtual meeting.

The Annual Meeting and any or all adjournments or postponements thereof will be held for the following purposes:

(1) To elect Carol A. Vallone, Andreas Krebs, Dr. Suzanne Bruhn, Dr. Roger Crystal, David Gryska, Roger Adsett and Robert Barrow to the Company’s board of directors (the “Board of Directors” or the “Board”) to hold office until the 2027 annual general meeting of shareholders (“Proposal No. 1”);

(2) To appoint KPMG LLP (“KPMG”) as independent registered public accounting firm (auditor) for the Company until the 2027 annual general meeting of shareholders (“Proposal No. 2”);

(3) To consider and, if deemed advisable, approve the amendment to the Definium Therapeutics, Inc. 2025 Equity Incentive Plan (the “2025 Equity Incentive Plan”) to increase the number of common shares available for issuance under the 2025 Equity Incentive Plan (“Proposal No. 3”) by 5,000,000 common shares; and

(4) To conduct any other business properly brought before the Annual Meeting and any adjournment or postponement thereof.

These items of business are more fully described in the proxy statement accompanying this Notice of Annual General and Special Meeting of Shareholders. The Annual Meeting will be held in a virtual format to enable greater participation by shareholders. At the Annual Meeting, all shareholders, regardless of geographic location and equity ownership, will have an equal opportunity to participate. Please attend the Annual Meeting at www.virtualshareholdermeeting.com/DFTX2026. Audio can be accessed via a phone, tablet or computer.

The record date for the Annual Meeting is April 15, 2026 (the “Record Date”). Only shareholders of record as of the close of business on that date may vote at the Annual Meeting or any adjournment or postponement thereof.

You may vote by submitting your proxy via the Internet, by telephone, or by mail by following the instructions on the proxy card or Notice by June 10, 2026 at 11:59 p.m. Eastern Time. If you are a beneficial owner of shares registered in the name of a broker, bank or other nominee, you should have received a voting instruction form with these proxy materials from that organization rather than from Definium. Simply complete and mail the voting instruction form in accordance with the instructions in that form to ensure that your vote is counted. Alternatively, you may vote by telephone or over the Internet by following the instructions provided by your broker, bank or other nominee. Beneficial owners should provide their voting instructions to their broker, bank or other nominee sufficiently in advance of the Annual Meeting and in accordance with the voting instructions provided by their broker, bank or other nominee.

Although not part of the proxy statement accompanying this Notice of Annual General and Special Meeting of Shareholders, we are also making available our 2025 Annual Report on Form 10-K, which includes our financial statements prepared in accordance with U.S. GAAP for the fiscal year ended December 31, 2025 (the “Annual Report”). The proxy statement, the proxy card and the Annual Report are first being made available online to shareholders beginning on or about April 27, 2026.

Important Notice Regarding the Availability of Proxy Materials for the

Annual Meeting to be Held on June 11, 2026 at 10:00 a.m. Eastern Time:

The proxy statement, the proxy card and the Annual Report are available at: www.proxyvote.com

You may also request paper copies of materials by the following methods:

Completing a request atwww.proxyvote.com; By telephone at 1-800-579-1639; or

By e-mailing sendmaterial@proxyvote.com and include 16-digit control number in the subject line.

By Order of the Board of Directors,

Robert Barrow

Chief Executive Officer

New York, New York

April 27, 2026

Your vote is very important to us. Whether or not you expect to attend the Annual Meeting, please complete, date, sign and return the enclosed proxy card or voting instruction form, or vote over the telephone or the Internet as instructed in these materials, as promptly as possible in order to ensure your representation at the Annual Meeting. Shareholders who attend the Annual Meeting should follow the instructions found at www.virtualshareholdermeeting.com/DFTX2026 to vote during the Annual Meeting.