  We introduce CRK-HACC, an extension of the Hardware/Hybrid Accelerated
Cosmology Code (HACC), to resolve gas hydrodynamics in large-scale structure
formation simulations of the universe. The new framework couples the HACC
gravitational N-body solver with a modern smoothed particle hydrodynamics (SPH)
approach called CRKSPH. $\underline{\text{C}}$onservative
$\underline{\text{R}}$eproducing $\underline{\text{K}}$ernel
$\underline{\text{SPH}}$ utilizes smoothing functions that exactly interpolate
linear fields while manifestly preserving conservation laws (momentum, mass,
and energy). The CRKSPH method has been incorporated to accurately model
baryonic effects in cosmology simulations - an important addition targeting the
generation of precise synthetic sky predictions for upcoming observational
surveys. CRK-HACC inherits the codesign strategies of the HACC solver and is
built to run on modern GPU-accelerated supercomputers. In this work, we
summarize the primary solver components and present a number of standard
validation tests to demonstrate code accuracy, including idealized hydrodynamic
and cosmological setups, as well as self-similarity measurements.
