Due to the combinatorial nature of molecules, chemical spaces can be very large . They are almost always too large to enumerate, let alone store. For drug-like molecules, the number has been estimated to be at least 10 33 . However, current molecules entering the clinic get more complex, and research into new modalities like PROTACs, which leads to molecules with larger molecular mass, indicates the our notion of what constitutes drug-like chemical space needs to be expanded, and previous size estimates are likely too conservative.