Identifying molecular mechanisms of exhausted CD8 T cells (T _ex ) is a key goal of improving immunotherapy of cancer and other diseases. However, high-throughput interrogation of in vivo T _ex can be costly and inefficient. In vitro models of T _ex are easily customizable and quickly generate high cellular yield, enabling CRISPR screening and other high-throughput assays. We established an in vitro model of chronic stimulation and benchmarked key phenotypic, functional, transcriptional, and epigenetic features against bona fide in vivo T _ex . We leveraged this model of in vitro chronic stimulation in combination with CRISPR screening to identify transcriptional regulators of T cell exhaustion. This approach identified several transcription factors, including BHLHE40. In vitro and in vivo validation defined a role for BHLHE40 in regulating a key differentiation checkpoint between progenitor and intermediate T _ex subsets. By developing and benchmarking an in vitro model of T _ex , then applying high-throughput CRISPR screening, we demonstrate the utility of mechanistically annotated in vitro models of T _ex .