We present Chandra and Very Large Array observations of GW170817 at∼ 521–743 days post-merger, and a homogeneous analysis of the entire Chandra data set. We find that the late-time nonthermal emission follows the expected evolution of an off-axis relativistic jet, with a steep temporal decay and power-law spectrum . We present a new method to constrain the merger environment density based on diffuse X-ray emission from hot plasma in the host galaxy and find . This measurement is independent from inferences based on jet afterglow modeling and allows us to partially solve for model degeneracies. The updated best-fitting model parameters with this density constraint are a fireball kinetic energy () and jet opening angle with characteristic Lorentz factor , expanding in a low-density medium with and viewed off-axis. The synchrotron emission originates from a power-law distribution of electrons with index . The shock microphysics parameters are constrained to and . Furthermore, we investigate the presence of X-ray flares and find no statistically significant evidence of≥ 2.5σ of temporal variability at any time. Finally, we use our observations to constrain the properties of synchrotron emission from the deceleration of the fastest kilonova ejecta with energy into the environment, finding that shallow stratification indexes α≤ 6 are disfavored. Future radio and X-ray observations will refine our inferences on the fastest kilonova ejecta properties.