Radio luminosity at 3 GHz vs. redshift from the S³-SEX semi-empirical simulation (Wilman et al. 2008) for a sky area of 20 × 20 deg² centred at the central coordinates of the simulation, and for a flux density limit of 17 μJy. We use a typically steep radio spectral index to convert the 1.4 GHz radio fluxes provided by the simulation into 3 GHz. Blue crosses are FRIs and red crosses FRIIs, and GPS sources are shown in black. We overplot the 3 GHz VLA-COSMOS survey as solid circles with red (FRII), green (FRI/FRII), blue (FRI) and black (COM AGN). We also show panels for each class, for clarity. The bar at the right side gives the number density of sources in the simulation. Bottom panel: GPS sources from the simulation and COM AGN from 3 GHz VLA-COSMOS survey, but a direct comparison cannot be made because COM AGN are not further classified as GPS.