T cells dynamically rewire their metabolism during an immune response. We applied single-cell RNA sequencing to CD8 ⁺ T cells activated and differentiated in vitro in physiological medium to resolve these metabolic dynamics. We identify a differential time-dependent reliance of activating T cells on the synthesis versus uptake of various non-essential amino acids, which we corroborate with functional assays. We also identify metabolic genes that potentially dictate the outcome of T cell differentiation, by ranking them based on their expression dynamics. Among them, we find asparagine synthetase (Asns), whose expression peaks for effector T cells and decays toward memory formation. Disrupting these expression dynamics by ASNS overexpression promotes an effector phenotype, enhancing the anti-tumor response of adoptively transferred CD8 ⁺ T cells in a mouse melanoma model. We thus provide a resource of dynamic expression changes during CD8 ⁺ T cell activation and differentiation, and identify ASNS expression dynamics as a modulator of CD8 ⁺ T cell differentiation.