Canon has just announced a firmware update, based on user requests, to the Canon EOS-1D X, which is available immediately.
Canon EOS-1D X firmware version 1.1.1 adds AF point illumination during AI Servo AF and cross-type AF for maximum apertures as small as f/8.
The AF Point Illumination during Servo Af is said to support the needs of wedding, portrait, sports, wildlife, and theatrical performance photographers working in low light. The users will better be able to aim the camera and select a focus point in low light conditions and when photographing dark subjects.
The Cross-Type AF Support at f/8 is said to be ideal for wildlife photographers and others who use Canon's EF super-telephoto lenses with tele-extenders, which cut down on the light reaching the sensor. The firmware increases the ability for the AF system to handle cross-type autofocusing with the center AF when the maximum aperture is only f/8, which will happen when using an f/5.6 lens with a 2x converter.
Go here to download Canon EOS-1D X firmware version 1.1.1.