Apple released tvOS 11.2 Developer Beta 3 on Monday, along with iOS 11.2 DB3, macOS High Sierra 10.13.2 DB3, and watchOS 4.2 DB3. This tvOS release cycle adds a developer API called AVDisplayManager for automatic display mode switching. It also brings back support for the Unwatched category in Home Sharing.
Apple has a support document explaining how to provision Apple TV devices for developer betas. More information can be found in the Apple Developer Connection.