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home / papers / 2026 / GM-PRM: A Generative Multimodal Process Reward Model for Multimodal Mathematical Reasoning

GM-PRM: A Generative Multimodal Process Reward Model for Multimodal Mathematical Reasoning

Paper · 2026 · Jianghangfan Zhang, Yibo Yan, Kening Zheng et al.

Summary

Multimodal LLMs often fail at multi-step math over images because one perception or logic slip in a single step derails the whole solution. Existing multimodal process reward models (PRMs) mostly label each step as right or wrong. They give little explanation and cannot fix the mistakes they find. The authors propose GM-PRM, a generative multimodal PRM. For each step it writes a critique covering three aspects: the step's purpose, its consistency with the image, and the validity of its logic. It also produces a corrected version of the first faulty step. This correction ability drives a new test-time procedure, Refined Best-of-N (Refined-BoN). The repaired step is fed back to the policy model, which then continues from a better starting point, so the candidate pool contains more varied and more accurate solutions. GM-PRM was trained on only about 20K curated examples, yet it reports state-of-the-art results on several multimodal math benchmarks. This suggests that critique-and-repair supervision can be highly data-efficient.

Key points

  • Training data: about 20K samples drawn from VisualPRM400K, mainly plane geometry and function problems. Step analyses and refinements were generated by GPT-4o and filtered with hard Monte Carlo estimation. The ViT encoder was kept frozen during SFT.
  • Step-level output: for every step, the model produces a textual critique and a "correct"/"incorrect" verdict, using both the problem image and its text.
  • WeMath, Best-of-8: Refined-BoN with GM-PRM outperforms Self-Consistency by 4.9 points on MiniCPM-V-2.6-8B, 3.5 on Qwen2.5-VL-7B and 4.1 on InternVL3-78B.
  • Scaling with N (MiniCPM-V-2.6-8B): the margin over Self-Consistency widens as N grows: 2.1, 2.2 and 4.9 points at N = 4, 6 and 8.
  • Limitations:
    • Only the first detected error is repaired.
    • Biases from GPT-4o labels may carry over into the model.
    • Gains may shrink on domains far from geometry and function problems, such as puzzles or proof-style reasoning.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

 Institutions

 Fields, topics and concepts

Cite

Cite as Jianghangfan Zhang, Yibo Yan, Kening Zheng, Xin Zou, Song Dai and Xuming Hu. 2026. GM-PRM: A Generative Multimodal Process Reward Model for Multimodal Mathematical Reasoning. Proceedings of the 4th Workshop on Advances in Language and Vision Research (ALVR).

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.18653/v1/2026.alvr-main.11

@inproceedings{zhang2026gm,
  title = {{GM-PRM: A Generative Multimodal Process Reward Model for Multimodal Mathematical Reasoning}},
  author = {Jianghangfan Zhang, Yibo Yan, Kening Zheng, Xin Zou, Song Dai and Xuming Hu},
  booktitle = {Proceedings of the 4th Workshop on Advances in Language and Vision Research (ALVR)},
  year = {2026},
  doi = {10.18653/v1/2026.alvr-main.11},
  url = {https://doi.org/10.18653/v1/2026.alvr-main.11}
}

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