Inferred atmospheric helium mass fraction as a function of the 1 bar temperature. Solid lines correspond to our baseline models for Jupiter and Saturn, using SR2018 with T_offset = 350 K. Dashed lines show similar evolution models but with T_offset = 650 K. The blue error-bar corresponds to the Galileo measurement of Y_atm (von Zahn et al. 1998) and the Voyager re-estimation of T_1bar (Gupta et al. 2022). Red errorbars (from top to bottom) correspond to estimates from Conrath & Gautier (2000),Koskinen & Guerlet (2018),Achterberg & Flasar (2020), Conrath et al. (1984) and the 1 bar temperature from Lindal et al. (1985). Black dots indicate specific ages in the evolution.