There are some caveats that Google mentions. They including the following...
- Some of the controllers listed above may require additional drivers in order to properly function with Stadia on Windows, MacOS, Linux, and ChromeOS.
- The “Home” button for the Xbox Adaptive Controller is not supported on Android, Linux, or ChromeOS.
- The “Home” button for Xbox controllers on Windows may open the Windows Game bar when pressed, and thus is not supported by Stadia on Windows.
- Bluetooth for Xbox One Wireless Controllers is not supported on Linux.
The above is also not an exhaustive list of controllers that can be used with Stadia, just the more popular ones. In addition, support further depends on the platform. Google breaks things down even further. Here's a look...
Outside of controller support, Google clarified several other details during its AMA session. Some of them are a bit disappointing. For example, only Chromecast Ultras that ship as part of a Stadia bundle will have the necessary firmware on launch day—existing Chromecast Ultra dongles that did not ship with Stadia will receive an over-the-air update "soon."
Google also clarified that Achievements will not be available at launch, though it looks like they will at least be tracked (and made visible through the UI sometime later).