arXiv AI By Chaoli Mou, Xinning Chen, Zhan Zhuang, Qinghe Zheng, Deyuan Kong, Yu Zhang

Selective Successor Eligibility Traces for RLVR

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The paper introduces Selective Successor Eligibility Traces (S-trace), a critic‑free eligibility trace method designed to improve temporal credit assignment in Reinforcement Learning with Verifiable Rewards (RLVR). S-trace reweights successor importance to recover downstream credit signals under PPO-style clipping and selectively propagates them to historical tokens using entropy-based token selection. Experiments on Qwen3 models show that S-trace yields significant absolute gains in average pass@16 over GRPO and trace-style GRPO, while also producing shorter responses.

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arXiv AI
Sep 15

HISPO: Hierarchical Importance-Sampling Policy Optimization with Entropy-Derived Segments

HISPO introduces a segment‑level policy‑optimization technique for reinforcement learning with verifiable rewards, creating entropy‑derived contiguous segments during rollout and applying clipped importance‑sampling correction at this granularity. It bridges the gap between token‑level and sequence‑level corrections, offering a middle‑ground approach for credit assignment in long‑form mathematical reasoning. Evaluated on Qwen3‑1.7B‑Base across six benchmarks, HISPO consistently outperforms or matches the strongest baselines in Pass@8 and Acc@8 metrics, notably improving AIME25 scores over GRPO and GSPO.

By Quoc-Vinh Lai-Dang, Hyo-Sang Shin