Performance. The evaluation metrics are shown in Table ; FaST significantly outperforms all baselines on all tasks including both single-property and multi-property optimization. On the most challenging task, GSK3β+JNK3+QED+SA, FaST improves upon the previous best model by over 30% in the product of the three evaluation metrics. Our model is able to efficiently search for molecules that stay within the constrained property space, and discover novel and diverse molecules by sequentially translating known and discovered active molecules. The MARS+Rationale model, which uses the same rationale molecules as the initialization for their search algorithm, does not perform well compared to the original implementation, which initializes each search with a simple "C-C" molecule.