Left panels: median triaxiality profiles for the fast rotators (top) and the slow rotators (bottom). The numbers on the left indicate the percentage of FRs or SRs populating each profile. The vertical dotted lines show r = 9 r_soft for TNG100 galaxies with M_* ∼ 10^10.3 M_⊙, the solid lines show r = 9 r_soft for TNG100 galaxies with M_* ∼ 10¹¹ M_⊙. At radii larger than these the profiles are not affected by resolution issues. Right panels: median of the stellar halo triaxiality distribution measured at 8 R_e as a function of stellar mass. The shaded areas are contoured by the 25th and 75th percentiles of the distribution. TNG100 and TNG50 are shown separately, FRs are on top, SRs on the bottom. On average the triaxiality parameter increases with radius and with stellar mass. The FRs have increasing T(r) profiles, while SRs have either constant or decreasing profiles.