The ability to build speaker groups that play music in your home is one of the best features of Google’s Assistant ecosystem. Now Google is allowing Android TV apps to be connected to a speaker party.
Google has apparently made it possible for all Android TV apps to function in groups of speakers. Most of the users who got this job were on Nvidia Shield TV models and I was able to check that on my device too.
Pointed out by @AndroidTV_rumor on Twitter, an easy way to get in on this updated version is to join the Chromecast Built-in beta on the Play Store. Within a little while, that should push the updated version to your device.