The performance of our model after each acquisition round was monitored with the help of nested 6-fold cross-validation. We observed that the (intrapolation) MAE consistently oscillated around the initial value of 0.52 kcal/mol (R 2 =0.78), and did not improve throughout the campaign (cf. Figure ). This however does not mean our model was not improving overall/becoming more robust: the accuracy of the predictions across the wider constructed chemical space rose rapidly, indicating improvements in the generalizability power across the chemical space of the model. From 1.15 kcal/mol in round one, the MAE on σ of the activation energy values gradually and monotonously decreased to 0.60 kcal/mol by round seven, i.e., the mean error was cut by over half its initial value. Starting from round five, a smooth leveling-off in the error reduction could be observed, and the prediction error in the final round approached the error obtained during (intrapolative) cross-validation. Both of these observations suggest that convergence had essentially been reached by this point.