System requirements are listed as "20 GB (Windows Store: 24.93 GB) (Steam:23.97GB)" however just to download Halo: Reach on Xbox Game Pass I am required to download 135.4GBs so I do not know where these numbers are from.
Game Pass lists 152.35GBs as "approximate size" and I assume this is for all the games.
Steam is also listed as 43GBs, though 25GB for Reach, so I am not sure what should be put down, and I don't own the Steam version either.