Apple has released tvOS 11.4 for Apple TV 4 and Apple TV 4K. It is available after a few weeks of developer and public beta testing. This update supports AirPlay 2 and iOS 11.4, which was also released yesterday.
Once you update to tvOS 11.4, any iOS users running iOS 11.4 should be able to see Apple TV 4 and Apple TV 4K in the Home app with other HomeKit devices.
Apple TV will make you assign a room when the update is complete. After this, you will be able to see “Now Playing” content and toggle playback on Apple TV using the Home app of your iPhone or iPad.
All speakers connected to Apple TV become speakers for AirPlay 2 as well. This provides you with the option to use Siri for playing music or podcasts on Apple TV in a specific room. This can be achieved via Siri on an iPhone, iPad, or even HomePod if you are running the latest software version. Sadly, Apple Watch and Mac are left out of the loop on this one.
With the power of AirPlay 2, Apple TV opens the possibility of playing multiple AirPlay 2 speakers at once. For instance, you can play the same audio from iOS or iTunes on different HomePods, Apple TVs, and other AirPlay 2 speakers simultaneously.
You can also use multiple speakers from Apple TV if you are running tvOS 11.4.