- Both lenses have Canon's most advanced coatings: Air Sphere Coating (ASC) and Super Spectra Coating (SSC) to cut down on ghosting and aberration, respectively.
- Image stabilization jumps to 5 stops of shake reduction, up from 3.5.
- Both lenses have shorter minimum focusing distances: 8.2 feet for the 600mm and 4.2 feet for the 400mm.
- Both use an arrangement of 17 lens elements in 13 groups.
- Heat shielding around the lenses prevents long exposure to high temperatures from deforming the elements.
- Front and rear elements have a fluorine coating to repel fingerprints and dust.
- The 400mm f/2.8L IS III USM will ship in December for $11,999.
- The 600mm f/4L IS III USM will ship in December for $12,999.