We will showcase our efforts building Julia proxy applications, or mini apps, targeting the Summit and Frontier supercomputers. We developed XSBench.jl to simulate on-node CPU and GPU scalability of a Monte Carlo computational kernel and, and RIOPA.jl for parallel input/output (I/O) strategies. We will share the lessons learned from Julia’s fresh approach for performance and productivity as a viable language, similar to Fortran, C and C++ for high-performance computing (HPC) systems.