As the library has grown, it's possible to imagine it becoming dominated by a small number of scaffolds that support facile elaboration, reducing diversity. This, however, has not been the case. As the library has added molecules, growing from hundreds-of-millions in ZINC15 to the current 4.5 billion, the number of Bemis-Murcko scaffolds has grown correspondingly and linearly with the overall database size. Over the past 5 years, for every 10 molecules added to the library, one new scaffold has been added (Figure ). Most of the scaffold diversity comes with the highest heavy atom count. Just the molecules in HAC24 and HAC25 contribute about twice as many scaffolds as all of HAC06-HAC23. The growth in library diversity has supported the ability to continue to discover novel scaffolds for targets, and the steady improvement in docking scores and affinities. .