was set to favor the exploration of the unknown regions, and a maximum of 15 points were acquired per round. Besides the acquisition function, we also applied a filter based on structural diversity, i.e., we required a minimal cosine distance between the fingerprints of new reactions being selected for acquisition. By applying this diversity filter, we ensured that the various reactive cores were each sampled as part of the campaign. The motivation for this approach stems from the observation that some cores intrinsically exhibit a higher σ than others; e.g. the highest value for the Diels-Alder reactions amounts to 6.68 kcal/mol, while for the [3,3] rearrangements, the highest value in the original BH9 subset amounts to a mere 5.15 kcal/mol. Without diversity-based filtering, we would have sampled almost exclusively reactions for the reaction cores resulting in the most divergent activation energy values in the initial dataset, and only minimal exploration would have been performed for the other cores at best. The settings of each acquisition round can be found in Section S2.1