X0202 SCHEDULE 13G/A 0001103804 XXXXXXXX LIVE 4 Common Stock, par value $0.0001 per share 03/31/2026 0001478320 Adaptive Biotechnologies Corp 00650F109 1165 Eastlake Avenue East Seattle WA 98109 Rule 13d-1(d) VIKING GLOBAL INVESTORS LP b DE 0 29993708 0 29993708 29993708 N 18.8 PN See Item 4 VIKING GLOBAL PERFORMANCE LLC b DE 0 22002189 0 22002189 22002189 N 13.8 OO See Item 4 Viking Global Equities II LP b DE 0 440046 0 440046 440046 N 0.3 PN See Item 4 Viking Global Equities Master Ltd. b E9 0 21562143 0 21562143 21562143 N 13.5 CO See Item 4 Viking Long Fund GP LLC b DE 0 7991519 0 7991519 7991519 N 5 OO See Item 4 Viking Long Fund Master Ltd. b E9 0 7991519 0 7991519 7991519 N 5 CO See Item 4 HALVORSEN OLE ANDREAS b Q8 0 29993708 0 29993708 29993708 N 18.8 IN See Item 4 Shabet Rose Sharon b X1 0 29993708 0 29993708 29993708 N 18.8 IN See Item 4 Adaptive Biotechnologies Corp 1165 Eastlake Avenue East, Seattle, Washington 98109 Viking Global Investors LP ("VGI"), Viking Global Performance LLC ("VGP"), Viking Global Equities II LP ("VGEII"), Viking Global Equities Master Ltd. ("VGEM"), Viking Long Fund GP LLC ("VLFGP"), Viking Long Fund Master Ltd. ("VLFM"), O. Andreas Halvorsen and Rose S. Shabet (collectively, the "Reporting Persons") Effective March 31, 2026, David C. Ott ("Mr. Ott") retired from his roles as Advisory Director of VGI and Executive Committee Member of each of Viking Global Partners LLC (the general partner of VGI), VGP and VLFGP. Accordingly, this Amendment No. 4 is being filed to remove Mr. Ott as a Reporting Person from this Schedule 13G, as Mr. Ott is no longer a beneficial owner of any of the shares of Common Stock reported herein. The business address of each of the Reporting Persons is: 600 Washington Boulevard, Floor 11, Stamford, Connecticut 06901. VGI and VGEII are Delaware limited partnerships; VGP and VLFGP are Delaware limited liability companies; VGEM and VLFM are Cayman Islands exempted companies; O. Andreas Halvorsen is a citizen of Norway; and Rose S. Shabet is a citizen of the United States. Y VGI: 29,993,708 VGI provides managerial services to VGEII, VGEM and VLFM. VGI has the authority to dispose of and vote the shares of Common Stock directly owned by VGEII, VGEM and VLFM. VGI does not directly own any shares of Common Stock. Based on Rule 13d-3 of the Securities Exchange Act of 1934, as amended (the "Act"), VGI may be deemed to beneficially own the shares of Common Stock directly held by VGEII, VGEM and VLFM. VGI beneficially owns 29,993,708 shares of Common Stock consisting of (i) 440,046 shares of Common Stock directly and beneficially owned by VGEII, (ii) 21,562,143 shares of Common Stock directly and beneficially owned by VGEM and (iii) 7,991,519 shares of Common Stock directly and beneficially owned by VLFM. VGP: 22,002,189 VGP, as the general partner of VGEII, has the authority to dispose of and vote the shares of Common Stock directly owned by VGEII. VGP serves as investment manager to VGEM and has the authority to dispose of and vote the shares of Common Stock directly owned by VGEM. VGP does not directly own any shares of Common Stock. Based on Rule 13d-3 of the Act, VGP may be deemed to beneficially own the shares of Common Stock directly held by VGEII and VGEM. VGP beneficially owns 22,002,189 of Common Stock consisting of (i) 440,046 shares of Common Stock directly and beneficially owned by VGEII and (ii) 21,562,143 shares of Common Stock directly and beneficially owned by VGEM. VGEII: 440,046 VGEII has the authority to dispose of and vote the shares of Common Stock directly owned by it, which power may be exercised by its general partner, VGP, and by VGI, an affiliate of VGP, which provides managerial services to VGEII. VGEM: 21,562,143 VGEM has the authority to dispose of and vote the shares of Common Stock directly owned by it, which power may be exercised by its investment manager, VGP, and by VGI, an affiliate of VGP, which provides managerial services to VGEM. Viking Global Equities LP (a Delaware limited partnership) and Viking Global Equities III Ltd. (a Cayman Islands exempted company), through its investment in VGE III Portfolio Ltd. (a Cayman Islands exempted company), invest substantially all of their assets through VGEM. VLFGP: 7,991,519 VLFGP serves as the investment manager of VLFM and has the authority to dispose of and vote the shares of Common Stock directly owned by VLFM. VLFGP does not directly own any shares of Common Stock. Based on Rule 13d-3 of the Act, VLFGP may be deemed to beneficially own the shares of Common Stock directly held by VLFM. VLFM: 7,991,519 VLFM has the authority to dispose of and vote the shares of Common Stock directly owned by it, which power may be exercised by its investment manager, VLFGP, and by VGI, an affiliate of VLFGP, which provides managerial services to VLFM. Viking Long Fund LP (a Delaware limited partnership) and Viking Long Fund III Ltd. (a Cayman Islands exempted company), through its investment in Viking Long Fund Intermediate L.P. (a Cayman Islands limited partnership), invest substantially all of their assets through VLFM. O. Andreas Halvorsen and Rose S. Shabet: 29,993,708 Mr. Halvorsen and Ms. Shabet, as Executive Committee Members of Viking Global Partners LLC (general partner of VGI), VGP and VLFGP, have shared authority to dispose of and vote the shares of Common Stock beneficially owned by VGI, VGP and VLFGP. Neither Mr. Halvorsen nor Ms. Shabet directly owns any shares of Common Stock. Based on Rule 13d-3 of the Act, each may be deemed to beneficially own the shares of Common Stock directly held by VGEII, VGEM and VLFM. Mr. Halvorsen and Ms. Shabet each beneficially own 29,993,708 shares of Common Stock, consisting of (i) 440,046 shares of Common Stock directly and beneficially owned by VGEII, (ii) 21,562,143 shares of Common Stock directly and beneficially owned by VGEM and (iii) 7,991,519 shares of Common Stock directly and beneficially owned by VLFM. The percentages set forth herein are based on 159,697,221 shares of Common Stock outstanding as of March 31, 2026, as reported in the Issuer's quarterly report on Form 10-Q, filed with the Securities and Exchange Commission (the "Commission") on May 5, 2026. VGI: 18.8% VGP: 13.8% VGEII: 0.3% VGEM: 13.5% VLFGP: 5.0% VLFM: 5.0% O. Andreas Halvorsen and Rose S. Shabet: 18.8% VGI: 0 VGP: 0 VGEII: 0 VGEM: 0 VLFGP: 0 VLFM: 0 O. Andreas Halvorsen and Rose S. Shabet: 0 VGI: 29,993,708 VGP: 22,002,189 VGEII: 440,046 VGEM: 21,562,143 VLFGP: 7,991,519 VLFM: 7,991,519 O. Andreas Halvorsen and Rose S. Shabet: 29,993,708 VGI: 0 VGP: 0 VGEII: 0 VGEM: 0 VLFGP: 0 VLFM: 0 O. Andreas Halvorsen and Rose S. Shabet: 0 VGI: 29,993,708 VGP: 22,002,189 VGEII: 440,046 VGEM: 21,562,143 VLFGP: 7,991,519 VLFM: 7,991,519 O. Andreas Halvorsen and Rose S. Shabet: 29,993,708 Y N The response to Item 4 is incorporated by reference herein. Y Y Y Y EXHIBIT A - JOINT FILING AGREEMENT VIKING GLOBAL INVESTORS LP /s/ Scott M. Hendler 05/15/2026 VIKING GLOBAL PERFORMANCE LLC /s/ Scott M. Hendler 05/15/2026 Viking Global Equities II LP /s/ Scott M. Hendler 05/15/2026 Viking Global Equities Master Ltd. /s/ Scott M. Hendler 05/15/2026 Viking Long Fund GP LLC /s/ Scott M. Hendler 05/15/2026 Viking Long Fund Master Ltd. /s/ Scott M. Hendler 05/15/2026 HALVORSEN OLE ANDREAS /s/ Scott M. Hendler 05/15/2026 Shabet Rose Sharon /s/ Scott M. Hendler 05/15/2026 (1) Scott M. Hendler is signing on behalf of O. Andreas Halvorsen, individually and as an Executive Committee Member of VIKING GLOBAL PARTNERS LLC, on behalf of VIKING GLOBAL INVESTORS LP, and as an Executive Committee Member of VIKING GLOBAL PERFORMANCE LLC, on behalf of itself and VIKING GLOBAL EQUITIES II LP and VIKING GLOBAL EQUITIES MASTER LTD., and as an Executive Committee Member of VIKING LONG FUND GP LLC, on behalf of itself and VIKING LONG FUND MASTER LTD, pursuant to an authorization and designation letter dated February 9, 2021, which was previously filed with the Commission as an exhibit to a Form 13G filed by Mr. Halvorsen on February 12, 2021 (SEC File No. 005-49737). (2) Scott M. Hendler is signing on behalf of Rose S. Shabet, individually and as an Executive Committee Member of VIKING GLOBAL PARTNERS LLC, on behalf of VIKING GLOBAL INVESTORS LP, and as an Executive Committee Member of VIKING GLOBAL PERFORMANCE LLC, on behalf of itself and VIKING GLOBAL EQUITIES II LP and VIKING GLOBAL EQUITIES MASTER LTD., and as an Executive Committee Member of VIKING LONG FUND GP LLC, on behalf of itself and VIKING LONG FUND MASTER LTD, pursuant to an authorization and designation letter dated February 9, 2021, which was previously filed with the Commission as an exhibit to a Form 13G filed by Ms. Shabet on February 12, 2021 (SEC File No. 005-49737).