Phoronix article: https://www.phoronix.com/news/Steam-Machines-Frame-2026
Also listed here: https://store.steampowered.com/sale/hardware
Valve has already sent support for the new Steam Controller upstream: https://www.phoronix.com/news/New-Steam-Controller-SDL
They work really well in third-person games for camera control. I beat Elden Ring on a Steam controller; you have a lot more speed and precision than with a stick.