Left: rest-frame radio luminosity density at 5 GHz vs. the rest-frame optical luminosity density at 4400 Å for z > 5.5 QSOs with a radio detection in the literature. Diagonal lines indicate constant radio-loudness values. Adapted from Bañados et al. (2015). Right: radio loudness as a function of redshift for the z > 5.5 confirmed RL QSOs compared to an optically selected sample of RL QSOs at lower redshift (orange points; Zhu et al. 2020) and all the RL QSOs at z > 4 (yellow diamonds) known to date. The blue squares (circles) report z > 5.5 (> 6) sources in both graphs. The only confirmed z > 5.5 blazar (Belladitta et al. 2020) is reported with a green triangle. At lower redshifts we did not distinguish this class because not all sources have a reliable classification. The red star represents VIK J2318−3113.