The impurity prediction pipeline was designed on the basis of the different possible reaction types, with the reaction predictions done using ASKCOS . At first, we enumerated all possible reaction types and used that as the basis to develop the codebase to do single-step impurity prediction. Extending this to multi-step reactions, or impurity propagation, was a combination of using a super-set constituents reaction, and following all the impurities to n steps downstream from the point they were predicted. All impurity predictions were done using ASKCOS version 2022.07, with the application programming interface (API) version 2.