X-ray luminosity versus bolometric luminosity for z > 6 QSOs (cyan symbols) from Connor et al. (2019, 2020), Vito et al. (2019a), Pons et al. (2020), and Wang et al. (2021a), compared with z < 6 QSOs (gray symbols) from Lusso et al. (2012), Martocchia et al. (2017), Nanni et al. (2017), and Salvestrini et al. (2019) and the L_X − L_bol relation (black dashed line) from Duras et al. (2020). Only radio-quiet QSOs are shown. Circles represent detected sources, and downward pointing triangles mark upper limits. PSO167–13 is shown in red. Diagonal dotted lines mark the loci of constant bolometric correction (i.e., K_bol = L_bol/L_X).