Cumulative 0.5–2 keV number counts at redshift z > 3 (left) and z > 4 (right). The number counts of the mock catalog we derived from the Vito et al. (2014)z > 3 XLF are plotted as a solid red line, while those of the mock derived using the Gilli et al. (2007) CXB model are shown using a dashed red line. The z = [3–5] number counts derived with the Ueda et al. (2014, dashed black line) model are also shown for comparison. Finally, the observational results from Chandra COSMOS Legacy (orange circles, Marchesi et al. 2016b) and from the CDF-S 7 Ms and CDF-N 2 Ms (green shaded area highligting the 68% confidence region; Vito et al. 2018) are also plotted for comparision.