LLM CoTs are often post-hoc rationalization; CRoS reward boosts faithfulness by 13.8%

mohitban47 · x · 2026-11-03

A paper by codezakh and XiaoYuUNC reveals key facts about LLM chain-of-thought: 1) LLM reasoning is often post-hoc rationalization — the model likely didn't use the CoT to derive its answer; 2) standard RLVR encourages such acausal reasoning, while rewarding causal CoTs improves accuracy and generalization; 3) checking causality of reasoning remains an open problem; 4) safety-wise, causally-trained models show more faithful, easier-to-monitor reasoning. Their CRoS (Causality Reward on Scrambled CoTs) method exploits the idea that scrambling reasoning steps should change answer probability if reasoning is causal. On Gemma-3-4B, CRoS improves CoT faithfulness by 13.8% while also improving accuracy and reasoning quality, mitigating the outcome-reward accuracy-vs-faithfulness trade-off.

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