Apple seeded tvOS 11.4.1 Developer Beta 2 on Monday. There are no new known features in this release cycle, as Apple has turned to development of tvOS 12.
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.