http://www.usa.canon.com/cusa/professional/products/professional_cameras/digital_slr_cameras/eos_6d#Features
High Performance Composing and Focus
The EOS 6D has an entirely new 11-point AF system for fast, accurate AF no matter the situation. With its new centered cross-type AF point with EV -3 sensitivity for improved performance and focus in low light, and a newly developed and bright 21mm eye point viewfinder with 97% coverage, the EOS 6D offers impressive performance in both composition and AF, even in the dimmest lighting situations. Offering not only One-Shot AF, AI Servo AF, and AI Focus AF, the EOS 6D’s AI Servo focus can be customized with tracking, acceleration and deceleration tracking sensitivities, and 1st or 2nd image priority adjustments. For even more customization, adjustment levels for the wide-angle and telephoto ends of particular lenses can be entered and recorded into the camera’s memory.
Only the center is cross typed. Minimum aperture @F5.6. No focusing @ F8.

Clearly this is not for sports or birders.
iFCL Metering with 63-zone dual-layering metering sensor
The EOS 6D features Canon’s multi-layer 63-zone iFCL (intelligent Focus Color Luminance) Metering System that integrates the camera’s AF system into its readings. By taking into account the color and luminosity surrounding the chosen AF point(s), this system delivers accurate results, especially in situations where the light changes quickly. The metering sensor enables evaluative, center weighted, partial and spot metering, plus offers 5-step exposure compensation for perfectly exposed images, every time.
High speed continuous shooting up to 4.5 fps allows you to capture fast action.
With continuous shooting speed up to 4.5 frames per second, the EOS 6D keeps up with the action. It is designed to capture the shots photographers want when shooting rapidly unfolding scenes.
EOS HD Video with manual exposure control and multiple frame rates
The EOS 6D captures HD video with a level of sophistication on par with professional movie cameras, offering phenomenal performance on a DSLR. It offers both All-I (UHS-I memory card is required) and IPB compression, supports H.264/MPEG-4 AVC High Profile, and automatically splits files greater than 4GB (FAT specifications) for extended recording without interruption. It offers the option of timecoding during recording only (Rec Run) or at all times (Free Run), useful for multi-camera shoots. It also features improved sound recording adjustment capabilities, offering 64-step volume control accessible through the Quick Control screen, as well as a 3.5mm microphone terminal. The CMOS sensor’s drive system significantly increases image processor performance, reducing color artifacts and moiré (a common problem that occurs in scenes with horizontal lines), and ensures that the EOS 6D can record at a number of frame rates up to ISO 25600 in H mode.