PALM-3000 is an upgrade to the current PALM-241 adaptive optics system at the 5.1 m Hale telescope which will allow
diffraction-limited science in visible wavelengths using bright natural guide stars, have more modest performance with
an upgraded Sodium laser guide star, and allow for guiding on faint natural guide stars. A key sub-system of the upgrade
is a new high-order Shack-Hartmann wavefront sensor with selectable pupil sampling, up to 64 subapertures across the
telescope aperture, to minimize wavefront reconstruction error for varying brightness of guide source with a frame rate
up to 3 kHz. The design and current status of the high-order wavefront sensing system is presented.