Apple has seeded tvOS 11.3 beta 3 to developers for testing. The build number is 15L5186e.
tvOS 11.3 includes new features, bug fixes, and security improvements in the OS and SDK, including:
● Enhancements to Match Content support.
● Automatic frame rate switching on Apple TV (4th generation).
● Automatic mode switching for AirPlay video sessions.
Notably, with an Apple TV and an iPhone on iOS 11.3, beta users can try out AirPlay 2.