Adaptive Biotechnologies Corp

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a)

of the Securities Exchange Act of 1934

Filed by the Registrant☒

Filed by a Party other than the Registrant☐

Check the appropriate box:

Adaptive Biotechnologies Corporation

(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 the appropriate box):

April 24, 2026

Dear Adaptive Biotechnologies Corporation Shareholder:

You are cordially invited to the Adaptive Biotechnologies Corporation 2026 Annual Meeting of Shareholders (the “Annual Meeting”). The attached proxy is solicited on behalf of the board of directors of Adaptive Biotechnologies Corporation for use at the Annual Meeting to be held on Friday, June 5, 2026, at 9:00 a.m., Pacific Time, or at any continuation, adjournment or postponement thereof, for the purposes set forth in the accompanying proxy statement, Notice of Annual Meeting of Shareholders (the “Notice”) and form of proxy. The Annual Meeting will be held entirely via the Internet, broadcast from our corporate headquarters at 1165 Eastlake Avenue East, Seattle, Washington 98109.

To be admitted to the Annual Meeting, you must register prior to Wednesday, June 3, 2026, at 5:00 p.m., Pacific Time at www.proxydocs.com/ADPT and enter the control number found on your proxy card, voting instruction form or Notice of Internet Availability of Proxy Materials you previously received. You may attend the meeting, vote your shares and submit questions electronically during the meeting via live webcast by registering at www.proxydocs.com/ADPT. You must also follow subsequent instructions you may receive by electronic mail thereafter. You may vote during the Annual Meeting by following the instructions available in the meeting access email. At the Annual Meeting, you will be asked to elect two Class I directors to our board of directors, to approve, on an advisory basis, the 2025 compensation of our named executive officers and to ratify the appointment of Ernst & Young LLP as our independent registered public accounting firm for the year ending December 31, 2026. The accompanying proxy materials describe these matters.

We have elected to provide access to our proxy materials on the Internet under the Securities and Exchange Commission’s “notice and access” rules. Our proxy materials are available at www.proxydocs.com/ADPT. We are mailing a Notice of Internet Availability of Proxy Materials on or about April 24, 2026, which provides instructions on how to access our proxy materials and our 2025 Annual Report on the Internet. Please read our proxy materials and our 2025 Annual Report carefully before submitting your proxy.

It is important that your shares are represented and voted at the Annual Meeting. You may vote on the Internet or by telephone as instructed in the Notice of Internet Availability of Proxy Materials or, if you are receiving a paper copy of the proxy materials, complete, sign and date the enclosed proxy card and return it in the enclosed envelope as soon as possible.

We thank you for your support and participation.

Sincerely,

Chad Robins

Chairman, Co-Founder and Chief Executive Officer

NOTICE OF 2026 ANNUAL MEETING OF SHAREHOLDERS

TO BE HELD ON JUNE 5, 2026

To the Shareholders of Adaptive Biotechnologies Corporation:

The attached proxy is solicited on behalf of the board of directors of Adaptive Biotechnologies Corporation for use at the Annual Meeting of Shareholders to be held on June 5, 2026, at 9:00 a.m., Pacific Time (the “Annual Meeting”), or at any continuation, adjournment or postponement thereof, for the purposes set forth below and in the accompanying proxy statement. The Annual Meeting will be held entirely via the Internet. Shareholders may participate in the Annual Meeting by registering at the following website: www.proxydocs.com/ADPT. You will need the control number included on your Notice of Internet Availability of Proxy Materials, your proxy card or the instructions that accompanied your proxy materials for the following purposes:

Proposal 1: To elect two Class I director nominees to serve on the board of directors of Adaptive Biotechnologies Corporation for a three-year term expiring at the 2029 annual meeting of shareholders. The nominees for election to the board of directors are Robert Hershberg, PhD, MD and Katey Owen, PhD;

Proposal 2: To approve, on a non-binding advisory basis, the compensation of our named executive officers as described in the proxy statement;

Proposal 3: To ratify the appointment of Ernst & Young LLP as our independent registered public accounting firm for the year ending December 31, 2026; and

To conduct any other business properly brought before the meeting or any adjournments thereof.

We know of no other matters to come before the Annual Meeting. Only shareholders of record of our common stock at the close of business on April 7, 2026 are entitled to notice of and to vote at the Annual Meeting or at any postponements or adjournments thereof. For ten days prior to the meeting, a complete list of the shareholders entitled to vote at the meeting will be available for examination by any shareholder for any purpose germane to the meeting during ordinary business hours at our executive offices located at 1165 Eastlake Avenue East, Seattle, Washington 98109.

YOUR VOTE IS IMPORTANT. PLEASE VOTE YOUR SHARES VIA THE INTERNET, THROUGH OUR TOLL-FREE TELEPHONE NUMBER (866-390-5390) OR BY SIGNING, DATING AND PROMPTLY RETURNING YOUR COMPLETED PROXY CARD. IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS FOR THE ANNUAL MEETING OF SHAREHOLDERS TO BE HELD ON JUNE 5, 2026: THIS PROXY STATEMENT, THE NOTICE OF ANNUAL MEETING OF SHAREHOLDERS AND THE ANNUAL REPORT ARE AVAILABLE AT WWW.PROXYDOCS.COM/ADPT.

By order of the board of directors,

Clarice McCauley

Vice President, Head of Legal, Corporate Secretary and Chief Compliance Officer

April 24, 2026

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PROXY STATEMENT