There is no demo at the moment for the XBox (or PC).
Last I heard a demo would not be out before the international release (last release is Jan 5th for North America). I don't know how much time before/after that will be devoted to the next patch, or how long it will take to create, test and release a demo. Actually, I don't recall Larian saying there would absolutely be a demo, but I would be surprised if there wasn't (at least for the PC).
