Apple has released the first public betas of iOS 11.4 and tvO 11.4, both of which add support for AirPlay 2.
AirPlay 2 is Apple’s followup to the original AirPlay Wi-Fi-based music playback standard. While Sonos popularized Wi-Fi-based multi-room audio playback, Bluetooth became ubiquitous, and multi-platform Wi-Fi audio standards spread in popularity, Apple lacked a competing story until AirPlay 2.
Messages in iCloud is also back in the iOS 11.4 beta. It allows you to store your iMessages in iCloud.