Apple releases iOS 11.4; update includes AirPlay 2 and Messages in iCloud
With AirPlay 2, music can be played in any room from any room
The new iOS build also includes AirPlay 2. This feature allows two HomePod units in the same room to stream music in stereo with individual left and right channels. AirPlay 2 also allows users to play music in any room from any room using an iOS device, HomePod, Apple TV or Siri. Music can be moved from one room to another, and different songs can be streamed in different rooms. AirPlay 2 is available now in the U.S., U.K. and Australia, and will rollout starting June 18th in Canada, France and Germany. Besides asking Siri to control the title of the songs playing, the rooms that they are playing in, and the volume, users can employ the Control Center to handle the same tasks.
The update to iOS 11.4 also adds calendar support for Apple's HomePod smart speaker. Bad news again for those in Canada, France and Germany; the calendar support for HomePod won't be available until later in the year.
You can check to see if iOS 11.4 is now available to be installed on your device by going to General > Software Update on your Apple iPhone or iPad.
The Control Center allows users to play different songs in different rooms, change the volume and more
source: Apple
Things that are NOT allowed: