Essential functions that sustain life including reproduction, signaling and mechanical motion, persist through the consump-tion of chemical fuels. Despite recent advances in developing dissipative assemblies that mimic such systems, the fuel-driven formation of covalent organic cages with the capacity to promote catalysis, folding, delivery and sequestration has yet to be demonstrated. In this work we describe the transient formation of a nanosized, tetrahedral cage (V = 5 nm3, Mw = 6150 Da) with four molecular baskets at its vertices linked via imine bonds to four aromatic amines forming the faces. Tribromo-acetic acid (TBA) acts as the chemical fuel that drives assembly of the cage via imine metathesis in addition to controlling its formation over time. Our study sets the stage for constructing large dissipative cages with spatiotemporal modes of opera-tion resembling the action of biological molecular machines.