Carbon capture and sequestration (CCS) from industrial point sources and direct air capture are necessary to combat global climate change. A particular challenge faced by amine-based sorbents—the current leading technology—is poor stability towards O₂. Here, we demonstrate that CO₂ chemisorption in γ-cylodextrin-based metal–organic frameworks (CD-MOFs) occurs via HCO₃⁻ formation at nucleophilic OH⁻ sites within the framework pores, rather than via previously proposed pathways. The new framework KHCO₃ CD-MOF possesses rapid and high-capacity CO₂ uptake, good thermal, oxidative, and cycling stabilities, and selective CO₂ capture under mixed gas conditions. Because of its low cost and performance under realistic conditions, KHCO₃ CD-MOF is a promising new platform for CCS. More broadly, our work demonstrates that the encapsulation of reactive OH⁻ sites within a porous framework represents a potentially general strategy for the design of oxidation-resistant adsorbents for CO₂ capture.