With the Exascale computers arriving at the DOE facilities, the ExaAM project1 will soon run its challenge problem. The ExaAM challenge problem is based on the NIST AMBench experimental builds and further characterization. These experiments both guide the model development and provide validation for the simulations. The project includes an integration of all the computational components of the AM process, where each component itself is an exascale simulation. What has emerged is that Exascale Computing will enable AM process modeling at the fidelity of the microstructure. This means tight coupling of Process-Structure-Property calculations. Macroscopic continuum codes (AdditiveFOAM) are used to simulation the metal melt-refreeze, within which mesoscopic codes (ExaCA, PFM) are used to simulate the development of material microstructure. This microstructure is then used by crystal plasticity codes (ExaConstit) to calculate local material properties. We present our coupled exascale simulation environment emphasizing the experiments we use to calibrate and validate the modeling. Work performed under the auspices of the U.S. Department of Energy by LLNL, LANL and ORNL under contracts DE-AC52-07NA27344, DE-AC52-06NA25396, DE-AC05-00OR22725, and supported by the Exascale Computing Project (17-SC-20-SC), a collaborative effort of the U.S. Department of Energy Office of Science and the National Nuclear Security Administration. REFERENCES [1] J.A. Turner, J. Belak, et.al, ExaAM: Metal additive manufacturing at the fidelity of the microstructure. The Int. J. of High Perf. Comp. App. (2022) 36: 13-39.