Comoving number density of M ≥ 10⁹ M_⊙ SMBHs hosted in jetted (orange line) AGN and in all AGN (blue line). The non-jetted curve is obtained from Shen et al. (2020). The radio-loud sample is instead composed by the Fermi/LAT (yellow squares and line) and Swift/BAT (red circles and line) all-sky catalogs. The bright green hexagons with thick black contours are lower limits to the z > 4 comoving number density of jetted sources derived by known blazars included in the spectroscopic SDSS+FIRST footprint, updated based on the results in this work. The less contrasted hexagons show instead the state of the art earlier than systematic searches of high-z blazars begun. Finally, the yellow diamond is the lower limit obtained by the detection of PSO J0309+27 (Belladitta et al. 2020). The data points obtained by systematic search and classification of blazar candidates are the lower limits, given that the search still ongoing.