A new post on Ubisoft's Support page breaks down the install space along with the size of the patch players will need to download on day one.
Xbox One and PC players with the physical version should expect a 48-52 GB download, with the overall install size for both physical and digital versions clocking in at 48-52 GB.
For reasons unknown, those who purchase the physical version on PlayStation 4 can expect a whopping 88-92 GB download. Regardless of physical or digital, the final install size on the HDD will be 88-92 GB.
Regardless of the platform you plan to play on, you're going to want to set aside a decent chunk of time to get the install and download done. It'd be a terrible shame to take the day off at launch, only to spend the majority of it staring at a download bar.
I can't for the life of me figure out why there is such a huge difference in size between the different formats. Do you have any ideas? Let me know in the comments below!