  Here we review the current conceptual optical mechanical design of GMagAO-X
--the extreme AO (ExAO) system for the Giant Magellan Telescope (GMT). The
GMagAO-X tweeter deformable mirror (DM) design is novel in that it uses an
optically distributed set of pupils that allows seven commercially available
3000 actuator BMC DMs to work "in parallel" to effectively create an ELT-scale
ExAO tweeter DM --with all parts commercially available today. The GMagAO-X
"parallel DM" tweeter will have 21,000 actuators to be used at ~2kHz update
speeds enabling high-contrast science at ~5 mas separations in the visible and
NIR of the spectrum (0.6-1.7 microns). To prove our concept for GMagAO-X
several items must be lab tested: the optical/mechanical concept for the
parallel DM; phasing of the GMT pupil; and solving the GMT's "isolated island
effect" will all be demonstrated on an optical testbed at the University of
Arizona. Here we outline the current design for this "GMT High-Contrast
Testbed" that has been proposed jointly by GMTO and the University of Arizona
which leverages the existing, operational, MagAO-X ExAO instrument to verify
our approach to phase sensing and AO control for high-contrast GMT NGS science.
We will also highlight how GMagAO-X can be mounted on the auxiliary port of the
GMT and so remain gravity invariant. Since it is gravity invariant GMagAO-X can
utilize a floating optical table to minimize flexure and NCP vibrations.

Instrumentation and Methods for Astrophysics;Earth and Planetary Astrophysics