As reported by VG247, the latest installment in the Forza Motorsport IP will need 100 GB of free space to launch.
There is no information yet why the latest game by Turn 10 will need that much space, but it may be connected to all those 4K gimmicks that Microsoft has promised. You can look at how the game looks in the trailer from the E3 conference:
Forza Motorsport 7 will launch October 3rd on PC and Xbox One. Start looking for that free space, motorsport lovers.