Apple 4K TV https://www.macrumors.com/2017/09/2
Post# of 96879
https://www.macrumors.com/2017/09/21/itunes-4...ming-only/
To stream 4K content to the new Apple TV 4K, Apple recommends a minimum speed of 25Mb/s, according to the support document. If an internet connection isn't fast enough, Apple will downscale the video quality.
In addition to the download restriction, one other major negative surfaced today -- the 4K Apple TV does not support 4K content from YouTube at this time. YouTube streams its 4K content using a VP9 video format, a codec the Apple TV does not support. The 4K Apple TV is limited to H.264, HEVC (H.265), and MP4.