Since its launch in 2008, the Fermi Large Area Telescope (LAT; Atwood et al. 2009) has enabled the discovery of new classes of gamma-ray emitters and the detection of much larger and better-characterized source populations than previously achieved. Active galactic nuclei (AGNs) represent by far the most abundant source population of the LAT detected sources. The 4LAC catalog (4LAC-DR1; Ajello et al. 2020), based on the 4FGL source catalog (4FGL-DR1; Abdollahi et al. 2020) established with 8 yr of data, comprised 2863| b|> 10 AGNs while 344 others were found at lower latitudes. As more data accumulate, the catalogs are regularly updated. Updates of 4FGL use the same data version (“P8R3”) and Galactic diffuse emission model as the initial catalog. Sources previously reported are kept in even if they fall below the TS= 25 threshold over the extended period of data taking. These sources retain their original positions, in contrast to new catalogs where all positions are reevaluated and subthreshold sources are omitted. The second data releases, 4FGL-DR2 (Ballet et al. 2020) and 4LAC-DR2 (comprising 285 new AGNs; Lott et al. 2020), were based on 10 yr of data.

Here we present the third update to the 4LAC catalog, derived from 4FGL-DR3 (Abdollahi et al. 2022) using 12 yr of data and comprising 1607 new sources relative to the initial 4FGL catalog. The properties of the 283 new 4FGL-DR2 69 and 308 new 4FGL-DR3 AGNs (DR2 and DR3 tallies will be aggregated in the following) are discussed. These AGNs are all blazars except for four radio galaxies. Besides providing a larger AGN sample for population studies, releasing periodic updates to 4LAC offers new targets for programs dedicated to classifying LAT blazars or measuring redshifts as detections come along (eg, Desai et al. 2019; Peña-Herazo et al. 2020, 2021a, 2021b; Peña-Herazo et al. 2021c; Goldoni et al. 2021; Rajagopal et al. 2021). The paper is organized as follows. Section 2 summarizes the analysis improvements introduced in 4FGL-DR3. Changes affecting 4LAC-DR1 AGNs are listed in Section 3. Section 4 presents the new DR3 sources, while Section 5 discusses the peak energy of the spectral energy distributions (SED) high-energy component, estimated from the spectral curvature, and the derived Compton dominance. A summary closes the paper in Section 6.