We determine the crystal structure and temperature of tantalum ramp- and shock-ramp compressed to hundreds of gigapascals at the National Ignition Facility. With x-ray diffraction, we find that tantalum remains in the body-centered cubic structure with no evidence for the proposed Pnma phase up to ramp-compression stresses of 531.7${}_{-18.7}^{+21.3}$,GPa. In separate experiments measuring single-shot extended X-ray absorption fine structure (EXAFS) at the L${}_3$ edge, we find that tantalum’s temperature agrees well with radiation-hydrodynamics calculations incorporating strength models for ramp- and shock-ramp compression to $$200,GPa, but not $$400,GPa. The discrepancy at $$400,GPa can plausibly be explained by underestimated ablation-plasma x-ray heating, with the magnitude of this heating increasing with laser irradiance. These results constitute the highest‐stress structural determination for Ta, the first L-edge EXAFS thermometry in ramp/shock‐ramp experiments, and a stringent benchmark of hydrodynamic models. They validate L‐edge EXAFS as a robust platform for thermometry in dynamic compression and underscore the need for careful ablator design in future high‐pressure studies.