Therapy resistance is the leading cause of cancer-related deaths. Polyploid cancer cells mediate resistance through adaptive cell states transitions that promote survival and tumor recurrence. Here, we investigate metabolic differences between cisplatin-surviving polyploid cells and parental cancer cells using integrated fluxomics. Transcriptomic and proteomic profiling and extracellular flux analyses revealed that surviving cells upregulate glycolysis and gluconeogenesis while reducing oxidative phosphorylation, indicating a shift in central carbon metabolism. Isotope tracing and metabolic modeling demonstrate that surviving cells utilize glucose to fuel the pentose phosphate pathway (PPP) for NADPH generation and metabolize glutamine to provide carbons for the PPP via gluconeogenesis. Integrating our multi-omic datasets into a genome-scale model identified that surviving cells sustain antioxidant metabolism by decreasing fluxes of other NADPH-consuming reactions upon in silico PPP knockout. In addition, pathway-centric transcriptomic analysis revealed that high PPP and antioxidant gene expression correlated with poor survival outcomes in patients across multiple cancer types, demonstrating the clinical prognostic value of PPP and antioxidant metabolism. These findings reveal a systems-level shift in metabolism that maintains antioxidant activity for cell survival, highlighting potential targets and treatment paradigms to overcome therapy resistance.