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EvaluationHard· Reasoning· Emergence· Optimization

Is the CoT length growth and backtracking observed in R...

Claims of emergent reasoning in R1-Zero should be treated with skepticism. The observed growth in CoT length is at least partially explained by biased GRPO objectives, where standard deviation normalization upweights near-zero-variance problems and length normalization creates incentives for longer responses when the answer is incorrect. Furthermore, backtracking phrases are present in the base model at non-zero temperatures, suggesting these behaviors are optimization artifacts rather than true emergent reasoning.

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