C'est dit dans l'annonce Canon présente sur le site US

The EOS-1D X includes a brand new 61-Point High Density Reticular AF, the most sophisticated DSLR AF system Canon has ever released. The 21 focusing points in the central area are standard precision cross-type and effective with maximum apertures as small as f/5.6, depending on the lens in use. The center five points are also high-precision diagonal cross-type points for maximum apertures as small as f/2.8. All 61 points are sensitive to horizontal contrast with maximum apertures as small as f/5.6 and 20 of the outer focusing points function as cross-type points with maximum apertures as small as f/4.0. Other innovations of the new 61-point High Density Reticular AF include expanded AF coverage area, superior focusing precision and low light sensitivity, and greater low-contrast subject detection capability compared to earlier EOS AF systems. (See image below for AF point configuration)