Spectral energy distribution (SED) of GRB 221009A at the epochs with available LHAASO data: 600–800 s (BIN-12; top panel) and 1000–1350 s (BIN-14; bottom panel). Since these two SEDs are right after prompt emission, in the early afterglow phase, they are individually modeled in a SSC scenario. The shaded yellow area represents the 1σ confidence intervals of the best-fit model. Figures B.1 and B.2 display the posterior parameter distributions for these two epochs. Table 4 and Table 5 enlist the best-fit model parameters and their associated uncertainties, respectively.