Halide exchange is a popular strategy to tune the properties of CsPbX3nanocrystals after synthesis. However, while Cl → Br and Br → I exchanges proceed through the formation of stable mixed-halide nanocrystals, the Cl ⇌ I exchange is more elusive. Indeed, the large size difference between chloride and iodide ions causes a miscibility gap in the CsPbCl3–CsPbI3system, preventing the isolation of stable CsPb(ClxI1–x)3nanocrystals. Yet, previous works have claimed that a full CsPbCl3→ CsPbI3exchange can be achieved. Even more interestingly, interrupting the exchange prematurely yields a mixture of CsPbCl3and CsPbI3nanocrystals that coexist without undergoing further transformation. Here, we investigate the reaction mechanism of CsPbCl3→ CsPbI3exchange in nanocrystals. We show that the reaction proceeds through the early formation of iodide-doped CsPbCl3nanocrystals covered by a monolayer shell of CsI. These nanocrystals then leap over the miscibility gap between CsPbCl3and CsPbI3by briefly transitioning to short-lived and nonrecoverable CsPb(ClxI1–x)3nanocrystals, which quickly expel the excess chloride and turn into the chloride-doped CsPbI3nanocrystals found in the final product.