In the image above, it shows that the Day One patch for Batman: Arkham Knight will be 3.5GB on PS4, so it is possible that is the same file size for Xbox One. This was also confirmed on Reddit, but has since been deleted. You’ll also need at least 45GB free just to install the game, without that patch.
If you have pre-ordered the game (Digital/Physical) or are planning on picking it up Tuesday make sure you have at least 50 GB free for your shiny new Batman game!