Now that Halo: Reach is out on PC, 343 Industries has shifted its attention to getting the next game in The Master Chief Collection into the hands of players on the platform. Seeing as how the series is landing on PC in the same order as they play out in the grand narrative, that means that Halo: Combat Evolved is next, and beta tests are set to start soon.
As detailed in this forum post, Halo Insider members (sign-up for that here) will be on the frontline as 343i and its partners get Master Chief's first outing up and running, with the first and second waves of testing taking place this month before more people are invited next month.
During these rounds of testing, players will be asked to check out a number of aspects, including dedicated servers, peer-to-peer connections, crossplay (Steam and Windows), and more. Those involved can expect to play a mixture of solo and co-op campaign missions and multiplayer.
The Anniversary edition of Halo: Combat Evolved launched in 2011 and is a part of Halo: The Master Chief Collection, alongside the aforementioned Reach, as well as Halo 2, Halo 3, ODST, and Halo 4.