  Context. As part of the third Gaia data release, we present the contributions
of the non-stellar and classification modules from the eighth coordination unit
(CU8) of the Data Processing and Analysis Consortium, which is responsible for
the determination of source astrophysical parameters using Gaia data. This is
the third in a series of three papers describing the work done within CU8 for
this release. Aims. For each of the five relevant modules from CU8, we
summarise their objectives, the methods they employ, their performance, and the
results they produce for Gaia DR3. We further advise how to use these data
products and highlight some limitations. Methods. The Discrete Source
Classifier (DSC) module provides classification probabilities associated with
five types of sources: quasars, galaxies, stars, white dwarfs, and physical
binary stars. A subset of these sources are processed by the Outlier Analysis
(OA) module, which performs an unsupervised clustering analysis, and then
associates labels with the clusters to complement the DSC classification. The
Quasi Stellar Object Classifier (QSOC) and the Unresolved Galaxy Classifier
(UGC) determine the redshifts of the sources classified as quasar and galaxy by
the DSC module. Finally, the Total Galactic Extinction (TGE) module uses the
extinctions of individual stars determined by another CU8 module to determine
the asymptotic extinction along all lines of sight for Galactic latitudes |b| >
5 deg. Results. Gaia DR3 includes 1591 million sources with DSC
classifications; 56 million sources to which the OA clustering is applied; 1.4
million sources with redshift estimates from UGC; 6.4 million sources with QSOC
redshift; and 3.1 million level 9 HEALPixes of size 0.013 squared degree, where
the extinction is evaluated by TGE.
