Beyond the Sampled Token: Preserving Candidate Support in RLVR

Ruotian Peng, Yi Ren, Zhouliang Yu, Weiyang Liu, Yandong Wen


Abstract
We revisit exploration collapse in reinforcement learning with verifiable rewards (RLVR), from the perspective of the candidate distribution for next-token prediction. We formally show that as probability concentrates on the top-1 candidate, the expected number of distinct responses collapses to one regardless of the sampling budget K. This theoretical implication is further verified by our empirical tracking of top-N candidate probabilities during training, where the top-1 candidate progressively dominates while plausible alternatives are suppressed. These findings suggest a key desideratum for effective exploration: preserving non-negligible probability mass on the top-N candidates. To this end, we propose Candidate-aware Support Preservation (CaSP), with two complementary designs. Specifically, CaSP redistributes positive gradients among top-N candidates for correct responses, and applies a stronger penalty to the top-1 candidate for incorrect responses. Unlike many exploration-oriented methods that improve pass@K at the cost of pass@1, CaSP improves pass@K across the full K spectrum. These gains generalize to 6 math, 2 logical-reasoning, and 2 coding benchmarks, and scales to 32B-parameter models and sampling budgets up to K=1024, positioning it as a principled, candidate-level approach for RLVR exploration.
Anthology ID:
2026.findings-emnlp.635
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:
13318–13340
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.635/
DOI:
Bibkey:
Cite (ACL):
Ruotian Peng, Yi Ren, Zhouliang Yu, Weiyang Liu, and Yandong Wen. 2026. Beyond the Sampled Token: Preserving Candidate Support in RLVR. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 13318–13340, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Beyond the Sampled Token: Preserving Candidate Support in RLVR (Peng et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.635.pdf