Along with iOS 11 beta 5, macOS High Sierra beta 5, and watchOS 4 beta 5, Apple released tvOS 11 developer beta 5 (build 15J5347f) on Monday. tvOS is the operating system that drives the fourth generation Apple TV.
It doesn’t look like there are any big changes in this developer beta, so presumably we’re looking at primarily bug fixes.
tvOS 11’s big feature—which isn’t available in the betas yet—is Amazon Prime support. It also offers automatic light and dark mode switching, plus support for AirPlay 2 and AirPods.