Target-Local Verifier Choice in Best-of-K Reasoning Selection

Xin Li, Hao Jiang, Weisi Lin


Abstract
Modern reasoning systems increasingly rely on verifier-guided selection: sample several solution traces, score them with a reward model, and return the top-ranked answer. In multi-generator deployments, this verifier is often reused across generators. We ask whether this reuse assumption is reliable. On a 34-generator math panel with K=64 candidates per problem and 7 verifiers, the 7B process reward model (PRM-7B) is the strongest fixed verifier, but a per-target single-verifier oracle gains +1.6 percentage points (pp). We then ask whether this target-local mismatch is actionable. Four label-free candidate-text statistics predict the coarse PRM outcome-verifier regime, and three budgeted responses improve over fixed PRM on the 22-target first-pass panel: a no-label gated router (+1.41 pp), PRM+V4 fusion (+2.35 pp), and a labelled PRM-only verifier-allocation arbiter (PVA-Adapt; +2.26 pp). A same-panel American Invitational Mathematics Examination (AIME) 2026 held-out slice gives +3.88 pp, and a second candidate-bank check keeps the scored and labelled gains positive while weakening the no-label router. We frame the result as a seed- and verifier-family-conditioned deployment diagnostic rather than a universal routing rule; a supervised fine-tuning (SFT) replication also finds no positive transfer from better selected traces.
Anthology ID:
2026.findings-emnlp.374
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:
7892–7915
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.374/
DOI:
Bibkey:
Cite (ACL):
Xin Li, Hao Jiang, and Weisi Lin. 2026. Target-Local Verifier Choice in Best-of-K Reasoning Selection. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 7892–7915, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Target-Local Verifier Choice in Best-of-K Reasoning Selection (Li et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.374.pdf