As promised, the Apple TV is finally starting to play YouTube videos in 4K — with caveats. Users on Reddit and elsewhere (via FlatpanelsHD and 9to5Mac) are starting to see YouTube 4K support enabled on the media hub when it’s using at least tvOS 14. However, you can only watch in Ultra HD at 30 frames per second, and without HDR. Don’t expect to make full use of that posh new TV just yet, although 60FPS video will play at up to 1440p.
YouTube confirmed the limitations to The Verge. It also said current iPads and iPhones should support 4K video with 60FPS and HDR, although support looks to be be inconsistent at this stage.