https://techcrunch.com/2018/05/29/airplay-2-and-homepod-stereo-pairing-arrive-with-ios-11-4/

iOS 11.4 arrives today, and with it, a bunch of welcome upgrades. The biggest updates here are, unsurprisingly, on the streaming media front, including the arrival of AirPlay 2, and the long awaited ability to pair up two HomePods for some stereo music living room listening.

Among other things, AirPlay 2 brings with it improved multi-room audio, so users can seamlessly move songs from one room to the next or just play the same music in all rooms at once on any iOS device, Apple TV or HomePod, via Siri. You can also play different music in every room, with requests like “Hey Siri, play Crowded House in the kitchen,” which should be a nice addition for families.