Same as Fig. 1, but for the virtual sub-Neptune motivated by GJ 436 b described in the text. The He I triplet line is one of the few atmospheric features detectable on sub-Neptunes with current technology (as in the case of GJ 3090 b, Ahrer et al. 2025). The limited set of simulations presented in this figure confirm that H₂ is likely to survive to far distances on them, which has a significant effect on the He I triplet line strength.