UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a)

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Adaptive Biotechnologies Corporation

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P.O. BOX 8016, CARY, NC 27512-9903 Adaptive Biotechnologies Corporation Important Notice Regarding the Availability of Proxy Materials Shareholders Meeting to be held on June 11, 2021 For Shareholders as of record on April 14, 2021 This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. This is not a ballot. You cannot use this notice to vote your shares. We encourage you to access and review all of the important information contained in the proxy materials before voting. To view the proxy materials, and to register to attend the meeting online and/or participate, go to: www.proxydocs.com/ADPT To vote your proxy while visiting this site, you will need the 12 digit control number in the box below. Under United States Securities and Exchange Commission rules, proxy materials do not have to be delivered in paper. Proxy materials can be distributed by making them available on the internet. For a convenient way to view proxy materials and VOTE go to www.proxydocs.com/ADPT Have the 12 digit control number located in the shaded box above available when you access the website and follow the instructions. If you want to receive a paper or e-mail copy of the proxy material, you must request one. There is no charge to you for requesting a copy. In order to receive a paper package in time for this year's meeting, you must make this request on or before June 01, 2021. To order paper materials, use one of the following methods. When requesting via the Internet or telephone you will need the 12 digit control number located in the shaded box above. * If requesting material by e-mail, please send a blank e-mail with the 12 digit control number (located above) in the subject line. No other requests, instructions OR other inquiries should be included with your e-mail requesting material. Adaptive Biotechnologies Corporation Meeting Type: Annual Meeting of Shareholders Date: Friday, June 11, 2021 Time: 09:00 AM, Pacific Time Place: Annual Meeting to be held live via the internet - please visit www.proxydocs.com/ADPT for more details. You must register to attend the meeting online and/or participate at www.proxydocs.com/ADPT SEE REVERSE FOR FULL AGENDA * E-MAIL paper@investorelections.com TELEPHONE (866) 648-8133 INTERNET www.investorelections.com/ADPT

Adaptive Biotechnologies Corporation Annual Meeting of Shareholders THE BOARD OF DIRECTORS RECOMMENDS A VOTE: FOR ON PROPOSALS 1, 2 AND 4 THE BOARD RECOMMENDS THAT AN ADVISORY VOTE ON THE COMPENSATION FOR NAMED EXECUTIVE OFFICERS BE HELD EVERY 1 YEAR. PROPOSAL 1. To elect three Class II director nominees to serve on the board of directors of Adaptive Biotechnologies Corporation for a three-year term expiring at the 2024 annual meeting of shareholders. 1.01 Michelle Griffin 1.02 Peter Neupert 1.03 Leslie Trigg 2. To approve, on a non-binding advisory basis, the compensation of our named executive officers as described in the proxy statement; 3. To approve, on a non-binding advisory basis, the frequency of future advisory votes on named executive officers' compensation; 4. To ratify the appointment of Ernst & Young LLP as our independent registered public accounting firm for our fiscal year ending December 31, 2021; and 5. The transaction of such other business as may properly come before the meeting.