Chimeric Antigen Receptor (CAR) T cell therapy has revolutionized cancer care, yet its manufacturing remains challenging due to variability in quality and efficacy. In this talk we introduce a novel microfluidic, label-free cellular biophysical profiling assay that rapidly assesses the functional phenotypes of CAR T cells. Our assay leverages biophysical features such as cell size and deformability to directly correlate with critical functional attributes, including the CD4:CD8 ratio, effector and central memory subtypes, and killing potency. Validated through extensive longitudinal studies across multiple CAR T batches from different donors and culture platforms, this method requires fewer than 10,000 cells and completes profiling within 10 minutes. The assay provides an efficient means to predict CAR T cell quality at critical manufacturing stages, thereby potentially reducing batch failure rates and enhancing therapeutic consistency.