When the Stadia service first launched, only the Chromecst Ultra devices that came with the Founder’s or Premier Edition supported the game service. Users with devices that were already in the field were left waiting for a firmware update to gain support.
Reports indicate that at least some Reddit users have now received a firmware update that adds support for Stadia to Chromecast Ultra devices that didn’t come with the Stadia editions. Users say that in most cases turning on Preview Program for the Chromecast Ultra and rebooting were all it took to get the new firmware.
The firmware that supports Stadia is version 1.42.180348. With that firmware installed, the user should see a working Stadia Controller linking code in the Ambient mode.
Only the Stadia Controller will work with the Chromecast Ultra for gaming. Some third-party controllers do support Stadia when connected to a Chrome desktop or mobile reports Android Police.