An internal beta for the Linux version of Steam will start next week and a private external test for 1,000 users will start later in October, according to Develop.
The external beta will include a test of Steam, one Valve title, and Ubuntu 12.04 and above support. It will not include Big Picture or other Valve games at first.
Valve hasn’t said which of its games will be tested, but it’s assumed to be Left 4 Dead 2 as it would be the first game Linux released for the service. the company previously said that Left 4 Dead 2 would be the first game rolled out on the operating system, making it likely this could be the title in question.
Experienced Linux users are encouraged to participate in the test, while Valve recommends newer Linux users wait for another round of testing which will contain new features and improvements.