https://www.cnet.com/news/ios-11-4-arrives-with-airplay-2-ahead-of-wwdc/

We're about a week away from seeing what iOS 12 will be like, but in the meantime the latest version of iOS 11 is here to download. iOS 11.4 is here, bringing an overdue feature promised last year: AirPlay 2.

AirPlay 2 is all about multi-room audio, and it also brings stereo dual-HomePod music playback to HomePods. AirPlay 2 will work on Apple TV, iPhones, and iPads.