Update: We're able to pre-load Infinite Warfare on Steam now (it wasn't showing up in our library earlier, but a restart fixed that), so we have more accurate sizes. On Steam, Infinite Warfare requires 74.2 GB, the Modern Warfare Remastered campaign requires 44.9 GB, and the Modern Warfare Remastered multiplayer requires 25 GB. So, that's about 144 GB total, nearly what's advertised on the Windows Store.
However, when actually downloading them, the files are 54.7, 21.7, 20.8 GB respectively, for a total of 97.2 GB for the whole package. Infinite Warfare, the Modern Warfare campaign, and the Modern Warfare multiplayer can all be downloaded separately. (Additional update: Now that I have unpacked the compressed Infinite Warfare download, which took nearly an hour, it's 70.3 GB.)
Original story: Call of Duty: Infinite Warfare is a very big game. Though it doesn't seem like its Windows Store entries are meant to be live yet (searching for them in the store returns nothing), we stumbled on them earlier today and found a few different versions of Infinite Warfare with size estimates of up to 149 GB.
On Steam, the system requirements ask for 70 GB of free space. The smallest estimate we found on the Windows Store, however, is 93.1 GB, which is for the basic edition of Infinite Warfare which doesn't include Modern Warfare Remastered.
The Digital Legacy and Digital Deluxe editions (which are also on Steam, but don't have their own pages) are estimated to be 149 GB on the Windows Store. Both of those editions include the Modern Warfare remaster, which the Windows Store estimates is 51.6 GB on its own, explaining how those bundles are so massive.
It's not clear on the Windows Store or Steam yet, but we assume that Infinite Warfare and Modern Warfare can be downloaded separately—though even then, 70-93 GB for just Infinite Warfare is pretty big. For comparison, The Elder Scrolls Online: Tamriel Unlimited asks for 68.4 GB when I install it on Steam, and GTA 5 wants 69.3 GB.
Another thing to note about the surprise Windows Store version that cropped up today: its multiplayer population won't be shared with Steam's. Not that we expect many were planning to buy the Windows Store versions we only just found out about and aren't being promoted for some reason.
Call of Duty: Infinite Warfare unlocks tonight, so we'll know better then—though we do plan to grab it from Steam. We don't have an early copy, so we'll update you along the way as we work on our review.