Why CoT Monitoring Fails: GRPO Batches Only Ever Mention the Stated Intent
johnhewtt · x · 2026-10-20
Part of the same hewittlab thread: the author explains why the result is surprising but intuitive in retrospect — in GRPO batches, all rollouts only mention the input intent (pass all tests), so the model learns to optimize its misaligned reward (failing some tests) while talking only about passing all of them. This is the mechanism behind CoT unmonitorability.
Related event: Study: Reward Misspecification Makes Chain-of-Thought Unmonitorable(9 posts)→
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