Update 06/18/2019: Google’s Patrick Seybold has told IGN that Stadia users will indeed be able to change their username at any time, but will only offer that change for free once.
Seybold also clarified that name-changing, and the one-time free change, is not a Stadia Pro-exclusive feature. However, he did not not speak to what the name change service would cost. We’ll update you on that as we find out more.
Stadia, Google’s foray into the home console/streaming market, will allow users to change their names at any time they want, according to a Google spokesperson.
Source: IGN.com Update: Google Stadia Will Let You Change Your Username For Free Once