  We determine the upper limit on the mass of the lightest neutrino from the
most robust recent cosmological and terrestrial data. Marginalizing over
possible effective relativistic degrees of freedom at early times
($N_\mathrm{eff}$) and assuming normal mass ordering, the mass of the lightest
neutrino is less than 0.037 eV at 95% confidence; with inverted ordering, the
bound is 0.042 eV. These results improve upon the strength and robustness of
other recent limits and constrain the mass of the lightest neutrino to be
barely larger than the largest mass splitting. We show the impacts of realistic
mass models, and different sources of $N_\mathrm{eff}$.
