https://wccftech.com/google-stadia-wi-fi-only/

Google Stadia launches in about a month if you’ve purchased the Founder’s or Limited Editions, but as we’ve already seen, early adopters will have to deal with a few quirks and limitations. The platform’s much-touted wireless controller will only actually be wireless if you’re playing via a Chromecast Ultra, connecting to any other device will require a USB cable, and now we have some bad news for folks who were hoping to play Stadia on their phone via their mobile network.

During an interview on The Vergecast, Google hardware chief was asked about playing Stadia via a mobile network, and he said “It’s just going to run on Wi-Fi to start.” Google later confirmed this to 9to5Google, saying they’re “focused on making sure Stadia Founders receive the best possible experience at launch over a Wi-Fi connection.”