Evolution of the molecular ISM out to z = 7.5. Left: molecular gas-depletion timescale (t_dep) as a function of redshift. Right: molecular gas-to-stellar mass ratio (μ_mol) as a function of redshift. The symbols are the same as in Fig. 4. Similarly, literature comparison samples are trimmed to fit the stellar mass range of the REBELS galaxies, M_stars = 10^{8.5–10 5} M_⊙. The open black squares represent the averages in each relevant redshift range.