The main differences, as far as I can tell, are that the bottom bracket on a cross bike is slightly higher (to clear obstacles), the tires are slightly wider with semi-knobby tires and the brakes allow for more mud clearance around the tire. There’s a slight difference in the frames as well, to make them easier to carry (a feature I don’t plan to take advantage of). Because the two are so similar it’s become increasingly common for people to have a separate wheelset with road tires, for a quick switch out. One thing I didn’t notice until I started checking out where the computer and GPS would go: The handlebars are narrower on a cross bike.