Treyarch thanked their optimization for the day one experience to allow a manageable download in todays AAA market. It seems that the 100GB - or 112GB to be precise - is simply required for the installation process, and the final size of the game will in fact be around 55GB.
Gamers with data-caps, be wary of Activision's Call of Duty: Black Ops 4 as the FPS juggernaut will have a colossal day one update. Remember when we reported that early copies won't work due to the game needing a Black Ops 4 day one update?
Treyarch claimed that it is serious about the PC version of Call of Duty: Black Ops 4, so it will be interesting to see whether the team has addressed the low-resolution textures in the Blackout mode, and whether it will run smoothly on various PC configurations. This update must be installed completely in order to access Multiplayer, Zombies, and Specialist Headquarters.
Red Dead Redemption II now holds the record with a massive 105GB install but Black Ops 4 has got nearly half that just for its day one patch - and the game won't work without it either.
The only upside is that Blackout, the new Battle Royale mode, becomes playable once the install is around 30% done.
According to Activision's support page, the day-one update has a download size of 50 GB, and when it's all done the game will leave a 55 GB footprint on your PlayStation 4 or Xbox One. If you've pre-ordered the digital version of the game then you'll be all set to go as the game will go live with the patch already included.
As for the PS4 and Xbox One version, they are also expected to get the preload 2 or 3 days before launch, so you should be able to download the game before it becomes available on October 12th.