Viking Global Investors LP Reports 18.8% Stake in Adaptive Biotechnologies Corp (ADPT)

This Schedule 13G/A (Amendment No. 4) filed on May 15, 2026, reports a combined beneficial ownership of 29,993,708 shares of Common Stock in Adaptive Biotechnologies Corp (ADPT) by Viking Global Investors LP (VGI) and its affiliates, representing 18.8% of the company. The reporting persons include Viking Global Performance LLC, Viking Global Equities Master Ltd., and Viking Long Fund Master Ltd., among others. The filing primarily serves to remove David C. Ott as a reporting person following his retirement on March 31, 2026, as he no longer holds beneficial ownership of the shares. VGI provides managerial services to the various funds and maintains shared voting and dispositive power over the reported shares. Principal control is exercised by O. Andreas Halvorsen and Rose S. Shabet as Executive Committee Members. The ownership calculation is based on approximately 159.7 million shares outstanding as of March 31, 2026. This represents a significant increase from the previously reported 0% holdings, establishing a major position for the Viking Global group.