Radio spectral index between 144 MHz (LoTSS-DR2) and 1.4 GHz (VLA FIRST) for the discovered quasars in the FIRST and VLASS survey area. Upper limits (indicated by downward-pointing triangles) are given for the quasars non-detected in FIRST. The dashed grey line shows the stacked spectral index obtained by Gloudemans et al. (2021a) using a sample of 115 known quasars at z >  5. ILTJ2201+2338 is outside of the FIRST footprint, but is detected in VLASS at 2–4 GHz, which enables a spectral index measurement. ILTJ1523+2935 is only marginally detected in FIRST (S/N ∼ 2), but is more securely detected in VLASS (S/N = 3.4).