At the time, Sonos did not specify which of its devices would support the new protocol, but Sonos has offered some clarification in the form of a new blog post that includes AirPlay 2 details.
According to Sonos, native AirPlay 2 support will be available on the Playbase, the newest version of the Play:5, and the Sonos One.
Older Sonos speakers will not support AirPlay 2 on their own due to processor limitations, but they can be paired with the Playbase, the Play:5, or the Sonos One to enable AirPlay 2 functionality. A Sonos Play:1 grouped with a Sonos One, for example, will support AirPlay 2.
The computing platforms and software architecture in some of the older Sonos players like Play:3 and Play:1 simply don’t have the horsepower to support AirPlay 2. The original Play:1, for example, has about 1/16th the processing power of its modern equivalent, the Sonos One. But by taking advantage of newer Sonos hardware, we’re able to make AirPlay 2 funtionality available throughout the house on speakers old and new.Apple thus far has not released AirPlay 2, despite the fact that it was first introduced as a feature of iOS 11 back in June of 2017. AirPlay 2 functionality was initially included in iOS 11.3 and tvOS 11.3 betas, but it was pulled ahead of the release of those updates.
AirPlay 2 functionality is now included in iOS 11.4 and tvOS 11.4, but it is not yet clear if the features will be included in the final version of the software.