Hardware specs aren't known yet, but Steam's website says it's worked with hardware partners to design 300 prototype Steam Machines are with "high-performance," which are "optimized for gaming, for the living room, and for Steam." And just like a PC, each Steam Machine will be open and upgradeable.
All Steam Machine prototypes will run hundreds of Steam games via Steam OS natively, and have access to the rest of the 3,000 titles on the platform.
In awesome Steam fashion, Valve is giving out all 300 Steam Machines to select users for testing — for free. The point of the Steam Machines beta is for Valve to learn what kind of form factors work best and what kind of features users want from a new living room gaming console box.
Once Valve has culled enough feedback, it'll launch the final Steam Machines made by different partners in 2014.
All you have to do to be eligible for the beta is fulfill a few missions by October 25. (Did you think you wouldn't have to do anything?) According to the Steam Machine FAQ, Valve will use two methods to select users: "A small number of users (30 or less) will be chosen based on their past community contributions and beta participation. The remainder will be chosen at random from the eligible pool."
Well, this is certainly going to make the living room console wars even more interesting next year.