Microsoft called the One X the "smallest Xbox ever." By two measurements it is, but barely: The new console is 5mm (0.2 inch) shorter and has a volume of 4,320 cubic centimeters, 90 cubic centimeters less than the Xbox One S.
Here you can see the rear of both units. Ports are identical: one front USB, two rear USB (with Kinect support with adapter); HDMI in and out; S/PDIF digital audio; Ethernet. The best news? Like the One S, the One X has an internal power supply -- no Buick-sized power brick like early Xbox models had.