  We reconstruct the Cosmic Microwave Background (CMB) lensing potential on the
latest Planck CMB PR4 (NPIPE) maps, which include slightly more data than the
2018 PR3 release, and implement quadratic estimators using more optimal
filtering. We increase the reconstruction signal to noise by almost $20\%$,
constraining the amplitude of the CMB-marginalized lensing power spectrum in
units of the Planck 2018 best-fit to $1.004 \pm 0.024$ ($68\%$ limits), which
is the tightest constraint on the CMB lensing power spectrum to date. For a
base $\Lambda$CDM cosmology we find $\sigma_8 \Omega_m^{0.25} = 0.599\pm 0.016$
from CMB lensing alone in combination with weak priors and element abundance
observations. Combination with baryon acoustic oscillation data gives tight
$68\%$ constraints on individual $\Lambda$CDM parameters $\sigma_8 = 0.814\pm
0.016$, $H_0 = 68.1^{+1.0}_{-1.1}$km s$^{-1}$ Mpc$^{-1}$, $\Omega_m =
0.313^{+0.014}_{-0.016}$. Planck polarized maps alone now constrain the lensing
power to $7\%$.
