Strings discovered in an APK teardown were found to refer to 4K, HDR and 5.1 sound - including toggles for adjusting the resolution on your "display" or "screen".
This has lead to 9to5Google making an educated guess that they refer to Android TV devices and sets, rather than mobile. There are relatively few mobile devices with 4K displays and the Android TV Stadia app has been popping up in others rumours recently, suggesting it is imminent.
Now that Stadia is available as a free service as well as the paid-for Pro, it makes sense to ramp up the number of devices that can access it. At present, you can only play Stadia cloud games on a TV using either a Chromecast Ultra or by plugging a PC or Mac into the HDMI port of a set.
Other new Stadia features found in the latest app's code strings include capture link sharing and text messaging.
Rather than having to download captured screens or video, you are likely to be able to share them with friends directly from within a future build of the Stadia app. And, messaging will be enabled to chat with friends without the need for voice.
You can find out much more about Stadia and the list of games available now and in future in our extensive round-up here: Google Stadia pricing, free trial, availability, games list, compatible devices and how it works.