The ANI-1ccx data set leverages a higher level of theory, CCSD(T)*/CBS (special extrapolation scheme to CCSD(T)/complete basis set), for a subset of the ANI-1x data points. The selection process began with a random subset of ANI-1x data, for which CCSD(T)*/CBS reference data was generated. An ensemble of models was trained on this CCSD(T)*/CBS data, and ρ was calculated for all remaining ANI-1x data points. Data points with ρ values exceeding a predetermined threshold were then selected, and CCSD(T)*/CBS data for these points was generated and added to the training set. This iterative process continued until the final ANI-1ccx data set was established.