With well-trained policy models, the optimisation results improved over the iterations. The statistics of the expected costs of molecules from the biological reactions pool over the 20 iterations is shown in Figure , and the chemical and hybrid reaction pathways show similar optimisation trends (Figure ). At iteration 0, the median of expected costs for all target molecules reaches approximately 100, which means in most cases, the random sampling 'decision maker' picks dead-end molecules to build reaction routes for the target molecules.