https://techcrunch.com/2019/06/06/heres-how-google-stadia-performs-depending-on-your-internet-connection/

Google is introducing more about the launch of its Stadia streaming gaming service today, and VP Phil Harrison gave us performance specifics today so you can see exactly how the company thinks the service will perform based on what kind of internet connection you have. It tops out at an impress 4K resolution, with HDR color, 60fps frame rate and 5.1 surround sound, but you’ll have to have at least a 35 Mbps connection to get that level of quality.

Meanwhile, at 20 Mbps you’ll get full HD 1080p output, while retaining HDR video, 60fps and 5.1 surround. And Google has optimized for smoothness of stream by retaining 60 fps all the way down to its recommended minimum bandwidth connection quality of 10 Mbps (and even potentially below that based on this chart). You’ll only get 720p streams at that level, however, and stereo instead of surround sound.