The Left 4 Dead Blog has word that the Linux beta build for Left 4 Dead 2 is now available. This can balance the fact that there seems to be an error in the report we shared the other day about Linux betas for Portal and Portal 2 also being available, as while Portal is now out for Linux, Portal 2 is not (apologies for the confusion). Here's word on the Linux L4D2 beta:

Thanks to the efficiencies we were able to achieve with Linux, we skipped Valve time and are delivering the L4D2 Beta Linux build today as planned. The Beta build not only allows Linux owners to play the game natively, it is also the testing ground for our new Extended Mutation System.

If you currently own Left 4 Dead 2, You should see “Left 4 Dead 2 Beta” in your library. If it doesn’t show up, restart Steam. This is a complete build of Left 4 Dead 2, so the build is as large as the current game.

You also receive access to the Left 4 Dead 2 Beta Authoring tools and Left 4 Dead 2 Beta Dedicated Server. This will allow you to start working with EMS.

The Beta version also contains updated Windows and Mac clients, so even if you are not running under Linux you can help by testing the Beta.