Rubric-Guided Process Reward for Stepwise Model Routing

Shenghao Ye, Yu Guo, Zhengheng Li, Qiang Huang, Shuangwu Chen, Wang Luo, Rui Qian, Jie Zhang, Tao Zhang, Dong Jin, Xiaobin Tan, Quan Zheng, Jianyang


Abstract
Stepwise model routing improves the efficiency of Large Reasoning Models (LRMs) by assigning each reasoning step to a suitable model. Recent methods formulate routing as a sequential decision process and train the router with reinforcement learning. However, although they model routing as a process, they still supervise the router with outcome rewards. Such rewards only reflect final answer correctness and fail to evaluate intermediate routing decisions, which can weaken performance and generalization. To address this gap, we propose RoRo, a rubric-guided process reward framework for stepwise model routing. RoRo first collects diverse routing trajectories and constructs preference pairs based on outcome, cost, and process quality. It then trains a Rubricor to generate a query-specific evaluation rubric and a Judge to score routing trajectories under this rubric through alternating optimization. The resulting process rewards are combined with outcome rewards to optimize the routing policy via GRPO. Experiments on five reasoning benchmarks under both same-family and cross-family settings show that RoRo consistently outperforms strong baselines and achieves better accuracy and cost trade-offs.
Anthology ID:
2026.emnlp-main.1222
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
27892–27910
Language:
URL:
https://aclanthology.org/2026.emnlp-main.1222/
DOI:
Bibkey:
Cite (ACL):
Shenghao Ye, Yu Guo, Zhengheng Li, Qiang Huang, Shuangwu Chen, Wang Luo, Rui Qian, Jie Zhang, Tao Zhang, Dong Jin, Xiaobin Tan, Quan Zheng, and Jianyang. 2026. Rubric-Guided Process Reward for Stepwise Model Routing. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 27892–27910, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Rubric-Guided Process Reward for Stepwise Model Routing (Ye et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.1222.pdf