  An incremental version of the fourth catalog of active galactic nuclei (AGNs)
detected by the Fermi-Large Area Telescope is presented. This version
(4LAC-DR3) derives from the third data release of the 4FGL catalog based on 12
years of E>50 MeV gamma-ray data, where the spectral parameters, spectral
energy distributions (SEDs), yearly light curves, and associations have been
updated for all sources. The new reported AGNs include 587 blazar candidates
and four radio galaxies. We describe the properties of the new sample and
outline changes affecting the previously published one. We also introduce two
new parameters in this release, namely the peak energy of the SED high-energy
component and the corresponding flux. These parameters allow an assessment of
the Compton dominance, the ratio of the Inverse-Compton to the synchrotron peak
luminosities, without relying on X-ray data.
