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
pretty sure it’s SteamOS, an Arch Linux derivative, on a fairly popular Snapdragon platform. probably not too difficult to hack on it.
It days right in the marketing text that the headset is “a PC” which to me implies full SteamOS distro with no limitations on installing a different OS, if you can get the many hardware drivers to work.
It says that it can run Windows applications so it might be the first VR headset that you can actually develop a game on.