We measure CP asymmetries and branching-fraction ratios for B± → DK± and Dπ± decays with D → K±π∓, where D is a superposition of D0 and 0. We use the full data set of the Belle experiment, containing 772 × 106 pairs, and data from the Belle II experiment, containing 387 × 106 pairs, both collected in electron-positron collisions at the Υ(4S) resonance. Our results provide model-independent information on the unitarity triangle angle φ3.