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Surveys in the 2020s comma notably the CMB-S4 program and Athena comma will reveal galaxy clusters at high redshifts comma all the way back to zvirgul3 comma when they first formed. Unveiling the properties openPardensity comma temperature comma entropy comma metallicityclosePar and evolution of the intracluster medium and the galaxy-halo connection in these early-forming systems will be among the primary science goals of both Athena and any Chandra successor. While many of the most exciting questions about the initial formation of galaxy clusters must wait for next-generation X-ray missions comma we can lay an important foundation now by extending studies of statistical cluster samples into the z>1 regime.