...is starting to roll out globally for Android. You need the Xbox Game Streaming (Preview) app on your phone from the Google Play Store, and you need your Xbox to be on a Preview Build Insider Ring.
I haven't got it working yet, my app on the phone says my Xbox isn't compatible. This could be because some sites are saying you need to be on an Alpha build, and I'm just on an Omega build. But we'll see how it goes, there's an official Reddit here where I'm sure the chatter will be helpful over the next few days:
and the MS site here: https://www.xbox.com/en-NZ/xbox-game-streaming/console-streaming
Haven't seen anything mentioned there about insider tiers yet.