RewardPartial: A Completion Potential Evaluation Framework for Truncated Best-of-N Paradigm

Xin Wang, Yidong Wang, Qiufeng Wang, Bo Jia, Yilin Niu, Jie Tang, Cunxiang Wang


Abstract
Traditional decoding-time alignment methods, such as Best-of-N sampling, enhance output quality by selecting high-reward responses from multiple candidates. However, these approaches incur substantial computational overhead, which limits their practicality. Recent advances aim to mitigate this inefficiency by scoring and filtering partial generations early in the decoding process. However, these methods face a critical challenge: conventional reward models (RMs), optimized to assess complete responses, exhibit poor performance when evaluating truncated text. To address this, we introduce RewardPartial, a novel evaluation paradigm that shifts the focus from superficial partial-text quality to estimating a response’s completion potential. We provide theoretical analysis for this paradigm through the perspective of Markov Decision Process and construct TruncEval, a specialized dataset for training RewardPartial models to accurately predict this potential. Our evaluation on the TruncEval test set demonstrates that RewardPartial models deliver significant performance gains over conventional reward models. When deployed in early-filtering pipelines, our method achieves superior alignment performance compared to Best-of-N sampling, offering a more efficient solution for high-quality text generation.
Anthology ID:
2026.findings-emnlp.488
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
10220–10234
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.488/
DOI:
Bibkey:
Cite (ACL):
Xin Wang, Yidong Wang, Qiufeng Wang, Bo Jia, Yilin Niu, Jie Tang, and Cunxiang Wang. 2026. RewardPartial: A Completion Potential Evaluation Framework for Truncated Best-of-N Paradigm. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 10220–10234, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
RewardPartial: A Completion Potential Evaluation Framework for Truncated Best-of-N Paradigm (Wang et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.488.pdf