We've known it's been coming for a while, but now the Apple TV finally supports 4K YouTube videos when it's running tvOS 14 or later. The update has been a long time in coming.
High Dynamic Range (HDR) isn't supported, however, which is a little disappointing given the Apple TV 4K's capability and the length of time this feature has taken to appear, while 4K will only play at 30fps. 1440p videos will play at 60fps.
The update was tested on both tvOS 14 - which is what we're running - as well as the new tvOS 14.2 public beta.
As for the iPhone and iPad, YouTube appears to offer 4K sometimes, but this isn't a given and it seems that YouTube 4K support will roll out properly to all iOS and iPadOS devices soon.
We're still expecting Apple to launch a new-generation Apple TV device soon as it seeks to push Apple TV+ further as a service. Apple is set to hold another launch event soon at which it will detail the iPhone 12, AirTags and possibly a new HomePod.