🤔 Rewarding correct answers doesn’t guarantee the model relies on the CoT, and LLM reasoning can often be post-hoc rationalization. Can we improve both accuracy and CoT faithfulness by optimizing CoT causality?
💡 Our key idea: If reasoning causally contributes to the final answer, changing the order of its steps should affect the probability of that answer. We propose CRoS (Causality Reward on Scrambled CoTs).
🔥 Outcome rewards improve accuracy at the cost of faithfulness, as models may learn shortcuts rather than rely on their CoTs. CRoS mitigates this trade-off, improving accuracy, reasoning quality, and faithfulness together!
⭐️ On Gemma-3-4B, CRoS improves CoT faithfulness (+13.8%), out-of-domain accuracy (+3.0%), and CoT quality (+2.0%) over the strongest outcome and causality reward baselines trained with GRPO.