Radio-loudness and brightness temperature relation of high redshift radio sources. Top left: The R_2500 Å index as a function of R_4400 Å for sources where both values are available in the literature. The dashed line represents R_2500 Å = R_4400 Å. Top right: The redshift-corrected L-band brightness temperatures as a function of radio loudness. The sources presented in this paper are marked with triangles. Bottom left: The redshift-corrected L-band brightness temperature measurements for all z > 5 AGN published to date, including those presented in this paper (triangles), as a function of redshift. Bottom right: The $R_{4400\mathrm{\AA }}=L_{5\mathrm{GHz}}/L_{4400\mathrm{\AA }}$ and R_2500 Å = L_5 GHz/L_2500 Å (where R_4400 Å is not available) radio-loudness indices of z > 5 sources as a function of redshift.