SteamOS was announced earlier this year as a project to bring yet more streaming to the living room. The Linux-based platform comes with Steam's Big Picture mode, allowing users to play titles through Steam with a controller.
Valve has selected 300 beta testers that will receive Steam hardware and SteamOS for testing.
SteamOS will be made available when the prototype hardware ships. It will be downloadable by individual users and commercial OEMs.