ChEMBL set compared to 9.5% of the heavy molecule set) shows that the heavy-molecule dataset is much more challenging. Thus, a significant improvement in computational clock-time was observed for both variants: 57% for dUCT-v1 and 20% for dUCT-v2. dUCT-v2 solved slightly more molecules, in ~20% less computational clock-time, with on average 0.6 more routes to a solved molecule than UCT.