Microsoft and 343 Industries are currently in the middle of another test of Halo: The Master Chief Collection, and as such has posted an update on Halo: Reach, the game currently under test and which will serve as the first game to be released in the collection.
The update gives us insight into how crossplay will work in Reach. There'll be support for Steam and Windows 10 editions, but there won't be any crossplay between the two PC editions and Xbox. That being said, you can share campaign progress across all 3 platforms, with the exception of mid-mission checkpoints and partially completed playlists.
Your stats will also be shared across all platforms, including achievements and leaderboards.
We also have an update on the system requirements, which are below;
There's still no details on when to expect a release, but we assume it'll be in the not too distant future if specs are being released.
You can read the full update here.