MADA-RL

MADA-RL: Multi-agent debate with counterfactual critic advantage for parameter-efficient reasoning in compact models

MADA-RL is a post-training framework that specializes compact LLMs (≤4B parameters) into generator and critic roles, training them with a debate-aware RL signal using LoRA adapters on only a small fraction of parameters. The central contribution is a counterfactual critic advantage that conditions the critic's reward on the generator ensemble's per-instance accuracy, explicitly incentivizing critics to correct generator errors rather than reproduce correct answers. Applied to DeepSeek-R1-Distill-Qwen-1.5B, the method achieves +2.0 percentage points on mathematical reasoning benchmarks using 16× fewer trainable parameters than fully fine-tuned baselines, placing it on the accuracy-vs-trainable-parameter Pareto front. The approach does not surpass the strongest baselines (DeepScaleR, STILL-3) trained on larger datasets, and the paper analyzes this gap directly.