use_qr_dqn was a hacky toggle that gated the IQN dual-head behind a num_atoms threshold. IQN is now always enabled when iqn_lambda > 0 (default 0.25). C51 remains the main loss; IQN is the auxiliary head for CVaR risk quantification. Removed use_qr_dqn from: DQNParams, DQNHyperparameters, fused_training, hyperopt adapter, all tests, all examples. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>