The sixth CCDC blind test featured molecule XXIII submitted by Pfizer Inc. which was a former research compound aimed at treating Alzheimer's disease. Three Z'=1 forms (A, B, D) and two Z'=2 forms (C, E) have been experimentally characterized and their relative stabilities are strongly dependent on temperature. The thermodynamically most stable form changes over a small range of temperatures in the following way: form C below 253 K, form B in 273 -288 K, form A in 290 -294 K, and form D at 295 K and higher. Many CSP approaches in the sixth blind test predicted form B to be the most stable among the three Z'=1 polymorphs. From our CSP calculations, candidate structures that match well with published structures for the three Z'=1 forms A, B, D (RMSD30 of 0.39, 0.23, and 0.18 Å in reference to CSD structures XAFPAY, XAFPAY01, XAFPAY03, respectively) are sampled and ranked among the top 30. We find that PBE-D3 favors form B as the most stable structure, similar to previous findings, and that r 2 SCAN-D3 and PBE0-MBD favor a predicted P-1 crystal structure not discovered by experiment (Figure ). Our computed temperature dependent stabilities correctly predicted form D to be most stable above room temperature, with form A very similar in energy as compared to form D across the temperature range (Figure (j) in SI).