Combined sample of TNG-Cluster (blue) and TNG300 (red), showing M_500c halo mass as a function of redshift. The mass assembly history of each z = 0 cluster is shown as a single line. For reference, we compare to observational samples of galaxy clusters from large surveys/survey instruments including Planck, ACT, ROSAT, and SPT (black markers; see text for details). Several notable low-redshift named clusters are also included for comparison in this mass-redshift plane – Virgo, Coma, Perseus, the Bullet Cluster, and El Gordo (points with errorbars; see text for details). The TNG-Cluster sample, in blue, is essential to compare to the most massive detected galaxy clusters, from z = 0 to cosmic noon.