Cast a Wider Net: Coordinated Pass@K Policy Optimization for Code Reasoning

Yilong Li, Suman Banerjee, Tong Che


Abstract
While repeated sampling against a verifier is the standard test-time compute strategy for code generation, measured by pass@K, drawing K independent samples from a single distribution often wastes the compute budget on redundant, near-duplicate reasoning paths. This failure is costly in competitive programming, where many problems admit multiple distinct algorithmic strategies and passing pass@K requires only one correct attempt. We propose **Coordinated Pass@K Policy Optimization (CPPO)**, which trains a joint planner–solver policy for pass@K: a planner emits a tuple of K=4 alternative high-level methods, and a shared solver attempts one solution per method. We train it with a multiplicative planner reward, Rplan = J𝜓 ⋅ Rout assigning credit only to valid strategy tuples that lead to verifier-confirmed pass@K success. Across APPS, CodeContests, and LiveCodeBench-v6, CPPO improves pass@4 over direct sampling, planning baselines, planner-only SFT, and pass@K-oriented RL under the same K=4 solver-attempt budget, with statistically significant gains on six of nine model–benchmark cells. For instance, it improves Qwen3.5-9B on LiveCodeBench-v6 from 0.588 with PKPO, the strongest baseline, to 0.728, an absolute gain of 0.14 under a hierarchical bootstrap test with p<0.05.
Anthology ID:
2026.emnlp-main.1701
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:
38736–38761
Language:
URL:
https://aclanthology.org/2026.emnlp-main.1701/
DOI:
Bibkey:
Cite (ACL):
Yilong Li, Suman Banerjee, and Tong Che. 2026. Cast a Wider Net: Coordinated Pass@K Policy Optimization for Code Reasoning. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 38736–38761, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Cast a Wider Net: Coordinated Pass@K Policy Optimization for Code Reasoning (Li et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.1701.pdf