Information content of the hot inner stellar halo across galaxy formation simulations. We show the correlations of M_{*, halo(r < 2 Re)} with the total ex situ stellar mass, M_*, ExSitu (left), and with the stellar mass accreted from the most massive merger, M_*, Ex1 (right), for different galaxy simulations. The thick black, blue, yellow, and green lines are the median curves from TNG50, TNG100, TNG300, and EAGLE galaxies at z = 0, respectively, in the M_* = 10^{10.3 − 11.6} M_⊙ range; the thin curves are the ±1σ scatters. The Pearson correlation coefficients, R, from the four sets of simulations are labeled in the corresponding colors.