On the matter of using old Chromecasts:
SourceA reminder that most existing (not-bundled) Chromecast devices will not support Stadia until they're updated over the next few weeks. You can check if your Chromecast Ultra can run Stadia by checking if it's running version
1.42.180348
or above. If your Chromecast is not on that version, attempting to play games on that Chromecast will fail until it receives the upcoming Stadia update. For now, we recommend using the Chromecast Ultra in your bundle to play.