The 343 Industries showed during their most recent Social Stream the work done so far in converting Halo Reach to PC.
During the broadcast, the studio, which is dedicated exclusively to the Halo series, spoke about the challenges of bringing Halo: The Master Chief Collection to PC. As announced in March, Halo Reach will be the first game in the collection to be released for PC.
If you do not want to hear the conversation, jump to the 10 minutes of the video, which is when the gameplay of the PC version of Halo Reach begins. You have almost 1 hour of gameplay to see.
The demo shown in this video is the same one that will be shown in E3 2019.