Once trained, the models can be used to generate target molecules conditioned on a source molecule by predicting one token at a time. Initially, the decoder processes the start token along with the encoder outputs to sample the next token from the probability distribution over all the tokens in the vocabulary. The generation process iteratively continues by producing the next token from the encoder outputs and all the previous generated tokens until the end token is found or a predefined maximum sequence length (128) is reached. To allow for the sampling of multiple target molecules, beam search is used (see Section 2.2), and unless otherwise stated, a beam size of 1, 000 was used.