According to official listings via the eShop and Nintendo website, the digital version of this revamped release (featuring brand new levels starring Shadow the Hedgehog) will require around 13.1GB of free space to install. The original Sonic Generations was around half the size of this on certain platforms.
You can also pre-order the digital version of Sonic X Shadow Generations right now. There's the standard version for $49.99 / £44.99 or the digital deluxe edition including skins, a BGM pack, digital artbook, and more for $59.99 / £54.99.
In some other Sonic X Shadow Generations news, the official Japanese Sega website has shared new screenshots showing off the Kingdom Valley Stage and the Modern Sonic Legacy Skin (thanks, Sonic Stadium). It's worth noting these screenshots are taken from other versions of the game.
Sega also recently revealed Sonic X Shadow Generations would come with a reversible cover sleeve, allowing fans to swap between the Western and Japanese box art.