By Mr. Brian Samas, Pfizer Molecule XXIII is the most experimentally characterized crystal structure prediction (CSP) blind test molecule to date. Crystal structures of five polymorphs are presented with corresponding stability data based on solvent-mediated phase transformation studies. In our phase transformation studies, we show that solubility is a crucial parameter. Computations reveal there is no strong dependence on the conformer distribution as a function of the solvent system. Position in the polymorph cascade is an important factor in predicting which form will be obtained in phase transformation experiments. Molecule XXIII remains the most important CSP example, and this work adds experimental backing and more precise transition temperatures between the forms.