[1-¹³C]pyruvate is the most widely used probe for hyperpolarized metabolic magnetic resonance imaging, with profound applications in tumor and inflammation diagnosis as well as treatment monitoring. The most fundamental hurdle to broader application, however, remains the rapid relaxation of polarization and the associated signal loss. Here, we report a method to address this challenge. Studying the nuclear spin relaxation dispersion of [1-¹³C]pyruvate across magnetic fields from 8 μT to 9.4T, as a function of additives, solvents, and preparation methods, allows us to achieve T₁ relaxation times of up to four minutes. Such a long T₁ could enable reliable quality control and nearly polarization loss-free transport, further boosting the power of hyperpolarized metabolic MRI. The power of the optimized protocol for T₁ elongation in vitro is showcased by more than doubling the sensitivity in a metabolic experiment.