In April, an third party software developer confirmed that Valve was working on porting its Steam download service, and its Source game graphics engine, over to Linux. This week, Valve itself has started talking about its Linux support plans with the launch of a new blog.
The first entry in the Valve Linux team blog says that formal work began in 2011 and that the Linux team now numbers about 11 people at Valve. The team's mission is to port games from Valve itself to Linux as well as "partner games". The team first set out to port Steam and Valve's zombie shooter Left 4 Dead 2 to the Ubuntu version of Linux.
Valve said there were two reasons to use Ubuntu:
First, we’re just starting development and working with a single distribution is critical when you are experimenting, as we are. It reduces the variability of the testing space and makes early iteration easier and faster. Secondly, Ubuntu is a popular distribution and has recognition with the general gaming and developer communities.
Valve said that it now has both the Steam client and Left 4 Dead 2 running natively on Ubuntu 12.04 and is now working on improving the performance. It will be providing development updates on a regular basis on the blog but there's no word yet on when the Linux projects will be released to the public.
Source: Valve Linux team blog