Developer and Apple sleuth Steve Troughton-Smith has managed to get Apple’s tvOS Simulator to run in 4K, the same screen resolution that’s been rumored for an upcoming fifth-generation Apple TV.
4K resolution is twice the standard HD resolution. Based on what Troughton-Smith has shared, tvOS appears to work fine in 3840 x 2160 resolution, with text, icons, and more scaling effectively to 4K.