Multiple metrics are computed at each epoch: the ratio of valid, accurate (only for fragmentbased models) unique or desired molecules, and the average arithmetic and geometric mean score per objective; and in the API users can define customised metrics. A compound is "desired" if it fulfils all objectives as defined in section 2.2.2. One of the metrics, by default the desirability ratio is used to select the best model epoch and to allow for early stopping. For fragment-based sampling, the inputs can either be a specific scaffold or the unique fragment combinations of a given dataset.