The all-inorganic metal halide perovskite CsPbI₃ is a promising photovoltaic absorber owing to its thermal stability and suitable bandgap for tandem applications. The most common approach to depositing CsPbI₃ from solution is based on the use of dimethylammonium iodide (DMAI); however, removing DMAI during crystallization is challenging, as it introduces residues that can lead to higher defect densities and trigger degradation. Here, we introduce a reaction-guided crystallization strategy based on 2,2,2-trifluoroethyl trifluoroacetate (TFTF), which undergoes a rapid ester-amine amidation reaction with DMAI during annealing. By converting DMAI into highly volatile products, the TFTF reaction drives a smooth, additive residue-free transition to γ-CsPbI₃ and produces pinhole-free films with low defect densities. Devices fabricated using this strategy deliver an open-circuit voltage (V_OC) of 1.20 V and a champion efficiency of 20.8%, along with markedly improved operational stability. This intermediate-management approach provides a practical, chemically defined pathway for directing CsPbI₃ crystallization and advancing high-performance inorganic iodide perovskite photovoltaics.