  We present the fourth Open Gravitational-wave Catalog (4-OGC) of binary
neutron star (BNS), binary black hole (BBH) and neutron star-black hole (NSBH)
mergers. The catalog includes observations from 2015-2020 covering the first
through third observing runs (O1, O2, O3a, O3b) of Advanced LIGO and Advanced
Virgo. The updated catalog includes 7 BBH mergers which were not previously
reported with high significance during O3b for a total of 94 observations: 90
BBHs, 2 NSBHs, and 2 BNSs. The most confident new detection, GW200318_191337,
has component masses $49.1^{+16.4}_{-12.0}\textrm{M}_\odot$ and
$31.6^{+12.0}_{-11.6}\textrm{M}_\odot$; its redshift of $0.84^{+0.4}_{-0.35}$
($90\%$ credible interval) may make it the most distant merger so far. We
estimate the merger rate of BBH sources, assuming a powerlaw mass distribution
containing an additive Gaussian peak, to be $16.5_{-6.2}^{+10.4}
(25.0_{-8.0}^{+12.6})$ Gpc$^{-3}$ yr$^{-1}$ at a redshift of $z=0$ ($0.2$). For
BNS and NSBH sources, we estimate a merger rate of $200^{+309}_{-148}$
Gpc$^{-3}$ yr$^{-1}$ and $19^{+30}_{-14}$ Gpc$^{-3}$ yr$^{-1}$, respectively,
assuming the known sources are representative of the total population. We
provide reference parameter estimates for each of these sources using an
up-to-date model accounting for instrumental calibration uncertainty. The
corresponding data release also includes our full set of sub-threshold
candidates.
