  We present the preliminary design of GMagAO-X, the first-light high-contrast
imager planned for the Giant Magellan Telescope. GMagAO-X will realize the
revolutionary increase in spatial resolution and sensitivity provided by the 25
m GMT. It will enable, for the first time, the spectroscopic characterization
of nearby potentially habitable terrestrial exoplanets orbiting late-type
stars. Additional science cases include: reflected light characterization of
mature giant planets; measurement of young extrasolar giant planet variability;
characterization of circumstellar disks at unprecedented spatial resolution;
characterization of benchmark stellar atmospheres at high spectral resolution;
and mapping of resolved objects such as giant stars and asteroids. These, and
many more, science cases will be enabled by a 21,000 actuator extreme adaptive
optics system, a coronagraphic wavefront control system, and a suite of imagers
and spectrographs. We will review the science-driven performance requirements
for GMagAO-X, which include achieving a Strehl ratio of 70% at 800 nm on 8th
mag and brighter stars, and post-processed characterization at astrophysical
flux-ratios of 1e-7 at 4 lambda/D (26 mas at 800 nm) separation. We will
provide an overview of the resulting mechanical, optical, and software designs
optimized to deliver this performance. We will also discuss the interfaces to
the GMT itself, and the concept of operations. We will present an overview of
our end-to-end performance modeling and simulations, including the control of
segment phasing, as well as an overview of prototype lab demonstrations.
Finally, we will review the results of Preliminary Design Review held in
February, 2024.
