3D electron diffraction reveals piracetam Form VI two decades after its computational prediction.

Crystal structure prediction often yields low-energy structures that lack experimental structural confirmation. Using 3D electron diffraction, we resolve predicted piracetam Form VI from a nanocrystalline powder mixture. Free-energy calculations place Form VI among ambient-accessible polymorphs and highlight machine-learning interatomic potentials as scalable tools for finite-temperature polymorph ranking.