As well as releasing the new iOS 11.4 software update Apple also released their new watchOS 4.3.1 update and their new tvOS 11.4 update.
The watchOS 4.3.1 software update brings some new features to the Apple Watch, although the update mainly includes performance improvements and bug fixes.
The tvOS 11.4 software update brings some new features to the Apple TV, these include support for Apple’s AirPlay 2. The update also comes with some bug fixes and performance improvements.
Both of these new updates are now available for the Apple Watch and the Apple TV. The Apple Watch update can be installed by using the Apple Watch app on your iPhone and the Apple TV update is available direct on the Apple TV.
Source Apple