The first beta test for Halo: Combat Evolved Anniversary's release on PC is coming up soon. Developer 343 Industries announced in a blog post (via Windows Central) that the first public test--or "flight" in the Halo vernacular--will begin in February.
You can sign up for the Halo Insider program for a chance to get into the testing phase.
Halo: Combat Evolved Anniversary is the second title within Halo: The Master Chief Collection that's coming to PC and other digital stores, following Halo: Reach at the end of 2019.
Microsoft is looking to test various elements of Halo: Combat Evolved, including the campaign (both solo and co-op), as well as multiplayer and its progression system.
In addition to launching the first Halo on PC, this next testing phase will include updates and improvements for Halo: Reach that Microsoft is testing before rolling out publicly. One of the updates is a feature that allows players to crouch while moving, which is supported on both mouse and keyboard and controller.
Halo: Combat Evolved Anniversary for PC will cost $10 USD on its own or $40 USD through The Master Chief Collection. A release date for Halo: Combat Evolved Anniversary's final version for PC hasn't been announced yet. The remaining titles in the package--Halo 2 Anniversary, Halo 3, Halo 3: ODST, and Halo 4--will release later. They will also be tested first through the Halo Insider program before launching publicly for everyone.
Part of the reason why Microsoft is being so thorough and extensive with its testing is because Halo: The Master Chief Collection got off to a horrible start on Xbox One back in 2014, and the company doesn't want to repeat those same mistakes. It's also worth noting that Halo: The Master Chief Collection is in a very good places these days with active player populations and ongoing support and updates.
2020 is a very big year for the Halo brand, as 343's other internal team is working on Halo: Infinite for release across Xbox One, Xbox Series X, and PC later this year.