An illustrated chronological story about how Canon autofocus systems and viewfinders went from a single AF point (1987) to 191 AF points (2020).
The number of AF points was increased, resulting in an 11-point AF system. One real innovation on this AF system was the increased low light sensitivity.
Each AF sensor is indicated with a small frame. The center is shaped as a uniform square whereas the remaining ten AF sensors are rectangles, oriented depending on their sensitivity. Again, note the smaller viewfinder coverage due to the full frame format of the camera.
The rectangular substrate is covered in transparent optical polymer just like previous sensors. While this is a new chip that has been redesigned (wire traces, bond wires, amplifier circuitry, etc.), the actual detector lines have an almost identical floorplan as the 9-point AF sensor used for the EOS 5D and EOS 5D Mark II. Interestingly, the 11-point AF sensor of the EOS 6D has various detector lines installed that could be used for up to eight Assist AF points arranged around the center AF point. However, there is apparently no documentation that the EOS 6D would actually use invisible auxiliary AF points. Rather, it can be assumed that the EOS 6D has such detectors on the hardware side, but that these are not used by the camera's firmware.
The center AF point is an f/5.6 standard-precision cross-type sensor (sensitive to both vertical and horizontal contrast lines) and f/2.8 high-precision horizontal sensor (sensitive to vertical contrast lines). Eight AF points are vertical sensors (sensitive to horizontal contrast lines) and two AF points are horizontal sensors (sensitive to vertical contrast lines) as shown in the illustration. Autofocus is not possible during viewfinder shooting with lenses having maximum apertures slower than f/5.6.
The system has an AF working range of EV -3 - 18 at ISO 100 at the center AF point and EV 0.5 - 18 at ISO 100 at all other AF points.