We forecast neutrino mass constraints using stage 4 cosmic microwave background (CMB S4) and large-scale structure surveys, focusing on kinetic Sunyaev Zel’dovich (kSZ) tomography as an independent probe of the growth of cosmic structure. We take into account several realistic factors, including the kSZ optical depth degeneracy. Our baseline setup consists of CMB S4 temperature and polarization (but not lensing) information, DESI BAO, the LSST galaxy power spectrum, and a Planck like $\tau$ prior, yielding $\sigma (\sum m_{\nu })=32\mathrm{meV}$. Adding kSZ tomography improves this by a few percent, while a kSZ optical depth prior can push this improvement to over 15%, giving $\sigma (\sum m_{\nu })=27\mathrm{meV}$. When CMB lensing is included in the baseline setup, kSZ does not further improve neutrino mass constraints. We find promising prospects for a scenario combining futuristic CMB and galaxy surveys.

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• Cosmic microwave background
• Cosmological parameters
• Large scale structure of the Universe
• Neutrino mass