Let's Verify Step by Step
Written for the Research library (claude-opus-5-5) from the paper text, in our own words: the license "arXiv — non-exclusive licence to distribute" does not allow redistributing the text itself. Original — arxiv.org/pdf/2305.20050v1
Summary
Language models that reason in a chain of thought still make logical slips, and one bad step can ruin a whole solution. The paper asks which kind of feedback produces a more trustworthy reward model for catching these errors. One option is outcome supervision (ORM), which judges only the final answer. The other is process supervision (PRM), which judges every intermediate step. The OpenAI team took GPT-4 models, further trained them on the MathMix math corpus, and had human annotators label each step of generated MATH solutions as positive, negative or neutral. Each reward model then picked the best answer from many sampled solutions. To get more value from labelling, annotators were mostly shown solutions that the current PRM rated highly even though their final answer was wrong. This is a form of active learning. The step-level verifier clearly outperformed the outcome-based one, solving 78.2% of a held-out MATH subset. Controlled smaller-scale experiments showed the same trend. The released PRM800K dataset makes research on step-level feedback much more accessible. The results also suggest that rewarding sound reasoning, not just correct answers, helps both accuracy and alignment.
Key points
- PRM800K: about 800K human step-level labels covering 75K model-generated solutions to 12K MATH problems. Evaluation uses 500 MATH test problems kept out of training.
- Best-of-N evaluation: the PRM scores a solution as the product of its per-step correctness probabilities. The best GPT-4-based PRM reaches 78.2% on the MATH subset, clearly ahead of the ORM.
- Active learning: showing annotators "convincing wrong-answer" solutions made process supervision about 2.6× more data-efficient.
- Cheaper ablations: small models, pretrained with about 200× less compute, were supervised by the large PRM instead of by humans. This allowed a fair comparison of ORM and PRM without new annotation.
- Relation to Uesato et al. (2022): that study found the two methods roughly equal on GSM8K. This paper argues the gap appears only with larger amounts of process feedback and on harder problems.
Cited by
- Many-Shot In-Context Learning
- Large Language Models for Mathematical Reasoning: Progresses and Challenges
- Llemma: An Open Language Model For Mathematics
- Qwen Technical Report
- Large Language Monkeys: Scaling Inference Compute with Repeated Sampling
- Weak-to-Strong Generalization: Eliciting Strong Capabilities With Weak Supervision
- InternLM2 Technical Report
- AlphaMath Almost Zero: Process Supervision without Process
- Do NOT Think That Much for 2+3=? On the Overthinking of o1-Like LLMs
- Towards Reasoning Era: A Survey of Long Chain-of-Thought for Reasoning Large Language Models
- FacTool: Factuality Detection in Generative AI -- A Tool Augmented Framework for Multi-Task and Multi-Domain Scenarios
- Process Reinforcement through Implicit Rewards
- DeepSeek-R1: Incentivizing Reasoning Capability in LLMs via Reinforcement Learning
- JudgeMeNot: Personalizing Large Language Models to Emulate Judicial Reasoning in Hebrew
- Cognitive Behaviors that Enable Self-Improving Reasoners, or, Four Habits of Highly Effective STaRs
- ToRA: A Tool-Integrated Reasoning Agent for Mathematical Problem Solving
- rStar-Math: Small LLMs Can Master Math Reasoning with Self-Evolved Deep Thinking
- V-STaR: Training Verifiers for Self-Taught Reasoners
- OpenRLHF: An Easy-to-use, Scalable and High-performance RLHF Framework
- Large Language Models Can Self-Improve
- Large Language Models Cannot Self-Correct Reasoning Yet
- Survey of Hallucination in Natural Language Generation
- Kimi k1.5: Scaling Reinforcement Learning with LLMs
- Training Language Models to Self-Correct via Reinforcement Learning
- Tulu 3: Pushing Frontiers in Open Language Model Post-Training
- Generative Judge for Evaluating Alignment
- LLMs-as-Judges: A Comprehensive Survey on LLM-based Evaluation Methods
- Search-o1: Agentic Search-Enhanced Large Reasoning Models
- MathVista: Evaluating Mathematical Reasoning of Foundation Models in Visual Contexts
- WizardMath: Empowering Mathematical Reasoning for Large Language Models via Reinforced Evol-Instruct
- Improve Mathematical Reasoning in Language Models by Automated Process Supervision
- Phi-4-Mini Technical Report: Compact yet Powerful Multimodal Language Models via Mixture-of-LoRAs
- s1: Simple test-time scaling
- OpenWebMath: An Open Dataset of High-Quality Mathematical Web Text
- DeepSeekMath: Pushing the Limits of Mathematical Reasoning in Open Language Models
- Scaling LLM Test-Time Compute Optimally can be More Effective than Scaling Model Parameters
- To CoT or not to CoT? Chain-of-thought helps mainly on math and symbolic reasoning
- ReFT: Reasoning with Reinforced Fine-Tuning
- Interpretable Preferences via Multi-Objective Reward Modeling and Mixture-of-Experts
- Math-Shepherd: Verify and Reinforce LLMs Step-by-step without Human Annotations
- InternVL3.5: Advancing Open-Source Multimodal Models in Versatility, Reasoning, and Efficiency
- Large Language Models are Better Reasoners with Self-Verification
- Inference Scaling Laws: An Empirical Analysis of Compute-Optimal Inference for Problem-Solving with Language Models
- The Rise and Potential of Large Language Model Based Agents: A Survey
- Logic-RL: Unleashing LLM Reasoning with Rule-Based Reinforcement Learning
- How Is LLM Reasoning Distracted by Irrelevant Context? An Analysis Using a Controlled Benchmark
- Qwen3 Technical Report
- Demystifying Long Chain-of-Thought Reasoning in LLMs
- MetaMath: Bootstrap Your Own Mathematical Questions for Large Language Models
- Scaling Relationship on Learning Mathematical Reasoning with Large Language Models
- SimpleRL-Zoo: Investigating and Taming Zero Reinforcement Learning for Open Base Models in the Wild
- Instruction Tuning for Large Language Models: A Survey
- Siren's Song in the AI Ocean: A Survey on Hallucination in Large Language Models
- Generative Verifiers: Reward Modeling as Next-Token Prediction
- ReST-MCTS*: LLM Self-Training via Process Reward Guided Tree Search
- The Lessons of Developing Process Reward Models in Mathematical Reasoning
- A Survey of Large Language Models
- ProcessBench: Identifying Process Errors in Mathematical Reasoning
- Solving Challenging Math Word Problems Using GPT-4 Code Interpreter with Code-based Self-Verification
- InternVL3: Exploring Advanced Training and Test-Time Recipes for Open-Source Multimodal Models
Cite
@misc{lightman2023let,
title = {{Let's Verify Step by Step}},
author = {Lightman, Hunter and Kosaraju, Vineet and Burda, Yura and Edwards, Harri and Baker, Bowen and Lee, Teddy and Leike, Jan and Schulman, John and Sutskever, Ilya and Cobbe, Karl},
year = {2023},
doi = {10.48550/arxiv.2305.20050},
eprint = {2305.20050},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.2305.20050}
}References
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