How does autobrake work?
Not all commercial jets have autobrakes, and the ones that do usually have a company policy dictating when it will be used.

The criteria for activating the brakes are different depending on the manufacturer and model of aircraft, but are typically some combination of:


System must be armed
A certain takeoff power setting must be set by the throttles
A certain airspeed must be obtained
Thrust levers must be pulled back to idle
Aircraft must still be on the ground


Usually for a rejected takeoff it does use max braking, however the autobrake usually has different settings for landing along the lines of "light/medium/max" braking.  Each setting will use a different amount of runway for landing, much like lightly pressing on the brake pedal in your car versus jamming it to the floor.