According to a preorder listing on the Japanese Playstation Store, Metal Gear Solid V: The Phantom Pain will actually take up less storage space that Metal Gear Solid 4. If you plan on downloading the game on Playstation 4, Metal Gear Solid V: The Phantom Pain will require 25.1GB of free space on your hard drive. Despite being an open-world game, it takes up less space than Metal Gear Solid 4: Guns of the Patriot. MGS4 takes up 26.6GB of space.
Konami hasn’t revealed why the file size is lower, but many believe it has to do with it’s real-time cutscenes and less audio.