The physical copy of Fallout 4 on the PC will still need a hefty download as the entire game is not on the disc.
While the game will ship on DVDs, it appears that buyers of the physical copy of Fallout 4 on the PC will still need an Internet connection in order to download the game Steam as the disc will not contain the entire game.
Vice President at Betheda Softworks, Pete Hines, posted that information on his Twitter account saying that "there is no data on the disc." While you will still use the disc to install the game the game "will still have to download from Steam" as "the disc doesn't contain the entire game."
The PC version of Fallout 4 will ship on multiple DVDs and although these could offer plenty of space, they are nowhere near much bigger Blu-ray discs that console version will ship on. According to Hines, the reason behind such a decision is to somehow prevent piracy.
Source:
Wccftech.com.