Apple seeded tvOS 11.4 Developer Beta 5 on Monday. This version of tvOS is testing AirPlay 2 through Apple TV 4 and Apple TV 4K devices.
tvOS is designed for Apple TV 4th and 5th generation devices, including Apple TV 4K. Installing developer betas of tvOS is a more complicated process than with other Apple devices. The company has a detailed how-to using both Xcode and Apple Configurator on your Mac.