There are several differences - first is stride length and cadence. In Chi Walking, the stride length always stays the same (short), while cadence gets faster as you increase your speed (and pelvic rotation increases with speed, as well). The other difference is arm position. In a slow meditative walk (about 55 strides per minute), the arms are almost straight, with a slight bend in the elbow. As you increase the cadence (to about 60-65), the elbows bend more, to about where your hands would go into your pants pockets. Above 65, the arm position is the same as in running - about a 90 degree bend - like a fitness walk.
So speed in walking is dependent on cadence, where as in running it’s dependent on the lean, and the cadence stays the same as your stride length opens up to the rear.
Hope that helps!
Certified Chi Running and Chi Walking Instructor