Valve Shipping Steam Machines and Making SteamOS Available for Download 12/13
You'll be to identify the beta participants by a special badge on their Steam Community profile. In addition to the badge (and hardware), those selected will also have a bunch of games added to their library that run natively on SteamOS.
Not without hiccups, regulatory red tape prompted Valve to limit the beta program to U.S. gamers only. Valve had hoped to launch the program worldwide, but decided it was better to run with it in the U.S. rather than delay the whole darn thing.
"We’ve had to make the difficult decision to limit our beta to the U.S. only, because of regulatory hurdles. This was not our original plan, and it means we can’t collect beta feedback from Steam customers worldwide, which is pretty unfortunate," Valve stated in a blog post. "All things considered, we’re sure it was the right decision, because the alternative was to delay the whole beta beyond the point when we’d be able to incorporate any feedback into the 2014 products. This decision only affects Valve’s 300 prototype units; the commercial versions of Steam Machines that are for sale in 2014 won’t be affected by this. More information on those will be announced at CES on January 6."
SteamOS will become available at the same time the prototype hardware ships out (December 13). Individual users and commercial OEMs will both be free to download the distro, though Valve recommends waiting until 2014 to try it out.