Fisher forecasted 1σ error bars on the sum of neutrino masses, Σm_ν, assuming a fiducial value at the minimum allowed sum of 60 meV. Different datasets are labeled on the left, with P16 corresponding to Planck 2015 data combined with the intermediate simlow likelihood, S4 corresponding to CMB-S4, BAO to DESI-BAO, and cvlowEE to a cosmic-variance-limited full-sky EE measurement up to ℓ  =  30. Orange error bars use the TANH reionization model, and blue errors bars are slightly degraded due to having marginalized over all possible reionization histories via the FlexKnot model. The black arrows show the expected shift when considering a flat knot prior vs. a flat τ prior.