As a first test of our methodology, we explore the performance of APC-tPBE on the Diels-Alder reaction between butadiene and ethylene. This reaction presents a well-studied series of transition states and intermediates that provide a clear challenge for automated multiconfigurational approaches, as all states contain a significant amount of multiconfigurational character (M > 0.1). Figure shows the tPBE results obtained with our automated APC (6,6) active spaces compared to previous literature results using hand-selected (6,6) active spaces, as well as reference MR-AQCC calculations. As is seen, the automatically selected active spaces are able to reproduce the tPBE results