Apple on Tuesday updated its mobile software to iOS 11.4. Along with cloud-based messages, this release also marks the official launch of AirPlay 2.

AirPlay 2 is the latest version of Apple's audio streaming system. AirPlay already allows music, podcasts and other audio to stream to the Apple HomePod smart speaker, Apple TV and additional AirPlay-compatible devices. 

This next-gen iteration adds two features we've been anticipating since WWDC 2017: multiroom audio and stereo sound. 

Multiroom audio means that you should be able to play the same audio on multiple HomePods or Apple TVs at the same time. 

Stereo sound enables you to set up two HomePods next to one other in the same room to improve the single HomePod's already-stellar sound quality.

In addition to controlling AirPlay from your iPhone or iPad's Control Center, you should also be able to enlist Siri to play your favorite party mix on more than one speaker. 

I saw a hint of this when I tested out the iOS 11.4 beta, but it was limited to Apple TVs. Even so, asking Siri to "play Bob Dylan in the gym and in the kitchen" worked during my preliminary testing of the TVOS beta.

AirPlay 2 is a necessary step for Apple to stay competitive in the smart home, but we've been waiting for its release for a year now. Both Amazon Alexa and Google Assistant smart speakers already offer multiroom audio. The Google Home Max, one of the HomePod's high-end competitors, already supports stereo pairing. 

Another potential setback for Apple is that the HomePod -- at $349 per speaker -- is prohibitively expensive for many people. That's compounded by the fact that both Amazon and Google offer $50 entry-level smart speakers. We haven't heard any updates on the rumor that Apple is working on a cheap HomePod, but it might be a good idea if HomePod sales are as slow as this Bloomberg report claims. 

We'd also like to see an update that improves Siri as a digital assistant to better compete with Alexa and Google Assistant. Apple is still far behind Amazon and Google in terms of smart home device partnerships, too.

I'm taking a fresh look at the HomePod review now that AirPlay 2 is out, so be sure to watch this space for the latest on all things related to Apple's Siri smart speaker.