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.
The public betas are available on Apple's Beta Software Program website. Just remember that beta software, so proceed with care. Apple does public betas in order to increase the size of the pool of testers. The tech giant recommends keeping back-ups of your files before installing a public beta.