Valve will start shipping its Steam Machines and Steam Controller to testers on December 13.
The machines are due to the leave the factory this Friday, December 13, and ship to the 300 selected beta participants.
Selected beta testers are being notified today and each will also be awarded a "special badge on their Steam Community profile," indicating that they’re a beta participant.
In addition, a number of games that run natively on SteamOS are being added to each selected user’s library.
"We’ve had to make the difficult decision to limit our beta to the U.S. only, because of regulatory hurdles," said Valve's Greg Coomer. "This was not our original plan, and it means we can’t collect beta feedback from Steam customers world-wide, which is pretty unfortunate.
"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 be made available when the prototype hardware ships and will be downloadable by individual users and commercial OEM. The in-home streaming beta is "to begin soon," as well according to Coomer.
During CES 2014 in January, the firm will be announcing its hardware partners for the Steam Machines along with device designs.