The announcement is short and sweet, and that’s all it needs to be. Linux gamers eager to play games from Valve and other developers natively can get on Steam now.
The Steam for Linux beta client is now available to all Steam users, so if you’ve been patiently waiting for an invitation to join us, consider yourself officially invited!
With a growing catalog of Linux-supported games, an active Steam for Linux community group, and a new GitHub bug reporting repository, the timing’s right to jump in and share your feedback.

Source: Steam | News Archive