  The Giant Magellan Adaptive Optics eXtreme (GMagAO-X) instrument is a
first-light high-contrast imaging instrument for the Giant Magellan Telescope
(GMT). GMagAO-X's broad wavelength range and the large 25-meter aperture of the
GMT creates new challenges: control of all 21.000 actuators; phasing GMT's
segmented primary mirror to nm levels; active control of atmospheric dispersion
to sub milli-arcsecond residuals; no chromatic pupil shear to minimize
chromatic compensation errors; integrated focal plane wavefront sensing and
control (WFSC). GMagAO-X will have simultaneous visible and infra-red WFS
channels to control the 21.000 actuator DM. The infra-red arm will be flexible
by incorporating switchable sensors such as the pyramid or Zernike WFS. One
innovation that we developed for GMagAO-X is the Holographic Dispersed Fringe
Sensor that measures differential piston. We have also developed several
integrated coronagraphic wavefront sensors to control non-common path
aberrations exactly where we need to sense them. We will discuss the key
components of the WFSC strategies for GMagAO-X that address the challenges
posed by the first high-contrast imaging system on the ELTs.
