• this method is used to train a new foundational molecular transformer model trained on what is, to the best of our knowledge, the largest ever data set of molecular pairs assembled, comprising of over 200 billion pairs. Some recent source-target models used 2 to 10 million pairs, while previous foundational chemical transformer models such as ChemBERTa were trained on approximately 100 million unique molecules. Contrastive-learning baselines are available at the 10 million molecule scale ;