What are the different possible AI takeoff speeds?

In a slow takeoff

AI capabilities improve gradually, giving us plenty of time to adapt. In a moderate takeoff we might see progress accelerating at a faster rate, but we still won’t be caught off guard by a dramatic change. In a fast or hard takeoff, AI quickly goes from being not very generally competent to being sufficiently superhuman to control the future. In a sufficiently hard takeoff there wouldn’t be enough time for humans to correct course if something goes wrong.

The article Distinguishing definitions of takeoff goes into more detail on this.