Hope wrote, "We're now using wireless prototype controllers to conduct live playtests, with everyone from industry professionals to die-hard gamers to casual gamers. It's generating a ton of useful feedback, and it means we'll be able to make the controller a lot better. Of course, it's also keeping us pretty busy making all those improvements. Realistically, we're now looking at a release window of 2015, not 2014.
"Obviously we're just as eager as you are to get a Steam Machine in your hands. But our number one priority is making sure that when you do, you'll be getting the best gaming experience possible. We hope you'll be patient with us while we get there. Until then, we'll continue to post updates as we have more stories to share."
That suggests Steam Machines won't be available until 2015, although the program's homepage still notes a 2014 release window. We've reached out to Valve for clarification.