A trusted hardware source with knowledge of Valve's Steam Machines project told PC Gamer at PAX East that Valve's Steam Controller will release in October or November of 2014.
The current, prototype version of the Steam Controller was refreshed in mid-March when Valve announced that it'd added two four-button button diamonds between the haptic trackpads.
Our source added that the completion of Valve's Steam Controller was the final piece that would precede the availability of most Steam Machines, which indicates that Steam Machines will also begin to release at the end of the year. The source also told PC Gamer that they expect “about 500” games to be natively playable on SteamOS by the end of this year, up from the current count of 382 .
We're looking forward to testing the Steam Controller and SteamOS in unison once both are fully released. Our last hands-on with the Steam Controller prototype at GDC didn't impress us.