The Xbox One Store has been updated earlier to confirm the file size for Call of Duty: Black Ops 4 on Xbox One at launch.
The Xbox One store states that Call of Duty: Black Ops 4 is set to be 42.6GB at launch as the approximate size. The lines up to previous Call of Duty games being around 50GB at launch, as the size will expand as the game gets new updates and post launch content to come for the title.
Pre-loading is not yet available for Call of Duty: Black Ops 4 on any platform, but is expected to start closer to launch for those who pre-ordered the title digitally on PS4, Xbox One, and PC. As a note, the file size will vary by platform and region, so we’ll update when we get confirmation of the size for PS4 and PC.
SOURCE: Xbox Store