Stacked posteriors for the five held-out development clusters, spanning 68 to 3870 Myr. Each panel shows the mean posterior across all stars in the cluster for GyroNet (solid blue), CHRONOFLOW (DASHED BLACK), and GYRO-INTERP (dotted orange), with the true cluster age marked by the vertical gray line. GyroNet produces the sharpest peak at the true age for M35, Hyades, and NGC 6819. For APer, GYRO-INTERP returns a flatter posterior, while both flow-based models recover the correct age. For M67, all three models peak near the true age, with GyroNet and ChronoFlow showing comparable precision.