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More than 90% of the world’s hydrogen (H₂) is produced from fossil fuel sources, which requires energy-intensive separation and purification to produce high-purity H₂fuel and to capture the carbon dioxide (CO₂) by-product. While membranes can decarbonize H₂/CO₂separation, their moderate H₂/CO₂selectivity requires secondary H₂purification by pressure swing adsorption. Here, we report hyperselective carbon molecular sieve hollow fiber membranes showing H₂/CO₂selectivity exceeding 7000 under mixture permeation at 150°C, which is almost 30 times higher than the most selective nonmetallic membrane reported in the literature. The membrane is able to maintain an ultrahigh H₂/CO₂selectivity over 1400 under mixture permeation at 400°C. Pore structure characterization suggests that highly refined ultramicropores are responsible for effectively discriminating the closely sized H₂and CO₂molecules in the hyperselective carbon molecular sieve membrane. Modeling shows that the unprecedented H₂/CO₂selectivity will potentially allow one-step enrichment of fuel-grade H₂from shifted syngas for decarbonized H₂production.