The Gaia SOS AGN work package aims at selecting and characterizing variable AGNs among the Gaia variable sources. This is obtained through the analysis of a number of properties, starting from those linked to variability. In particular, the structure function (SF; Simonetti et al. 1985) and the Butler and Bloom (2011) statistics, based on a damped random walk modelling of the SF, are known to be very effective in selecting AGNs from light curves.