Apple has seeded tvOS 11.3 beta 4 to developers for testing.. The build number is 15L5198d.
About tvOS 11.3 beta 4
tvOS 11.3 includes new features, bug fixes, and security improvements in the OS and SDK,
• Enhancements to Match Content support.
• Automatic frame rate switching on Apple TV (4th generation).
• Automatic mode switching for AirPlay video sessions.
Developers can download the new build of tvOS 11.3 from the link below. Please follow Gearsofbiz on Twitter, Facebook, Google+, or RSS for updates.