arXiv AI

A Sign Law for Entropy Drift under Sampler Mismatch in RLVR

The paper investigates how entropy behaves in reinforcement learning with verifiable rewards (RLVR) when the sampling method used during rollouts differs from the learner’s policy. It shows that a constant advantage shift alters the entropy of a softmax policy in a way that depends on the sampler: positive shifts sharpen the policy for samplers whose likelihood ratio increases with token probability (e.g., top‑k, top‑p, min‑p, and temperatures below one) and flatten it for flatter samplers. In group‑based RLVR with token‑level losses, the entropy drift is governed by the token‑weighted net advantage and a covariance term that can amplify over long horizons, with empirical results on 2B and 9B models demonstrating how different sampling and baseline strategies affect entropy stability and held‑out accuracy.

arXiv AI
6d ago

There Is No Free Lunch in RLVR: Every pass@1 Gain Has a pass@k Price

The paper proves that in reinforcement learning with verifiable rewards (RLVR), any improvement in pass@1 necessarily incurs a cost in pass@k, establishing a precise price for such gains. By modeling RLVR as an exponential tilt of a base policy, the authors show that every update that raises pass@1 strictly lowers success on at least one prompt, and that the number of pass@k crossovers is bounded by the sign variation of per‑prompt success shifts. The work also derives an entropy‑performance law and provides a diagnostic to measure this price from evaluation logs.

By Yinuo Liu
arXiv AI
Jun 18

STARE: Surprisal-Guided Token-Level Advantage Reweighting for Policy Entropy Stability

arXiv:2606. 19236v1 Announce Type: cross Abstract: Reinforcement Learning with Verifiable Rewards algorithms like GRPO have emerged as the dominant post-training paradigm for complex reasoning in LLMs, yet commonly suffer from policy entropy collapse during training.

By Haipeng Luo, Qingfeng Sun, Songli Wu, Can Xu, Wenfeng Deng, Han Hu, Yansong Tang
arXiv AI
Jun 19

Beyond Entropy: Learning from Token-Level Distributional Deviations for LLM Reasoning

arXiv:2606. 19771v1 Announce Type: new Abstract: Reinforcement Learning with Verifiable Rewards (RLVR) has significantly advanced Large Language Model (LLM) reasoning; however, it faces a fundamental optimization instability: uniform token updates precipitate entropy collapse, leading to premature convergence to suboptimal strategies, whereas excessive Shannon Entropy maximization can cause entropy explosion, driving blind exploration toward incoherent reasoning chains.

By Xuanzhi Feng, Zhengyang Li, Zeyu Liu, Haoxi Li, Yuming Jiang, Bing Guo, Jingcai Guo, Jie Zhang, Song Guo
arXiv Machine Learning
Oct 5

Planning to Learn

The paper introduces a new loss function called the horizon loss for training classifiers. It argues that the exact policy gradient used in reinforcement learning is myopic, whereas cross‑entropy is patient, and the horizon loss interpolates between the two by truncating the total error at the remaining learning. Experiments on MNIST and ImageNet with ResNet and ViT models show that horizon loss consistently improves top‑1 accuracy over cross‑entropy, especially when label noise is present.

By Ian Osband
arXiv AI
Aug 3

Deconstructing Off-Policy Ratios: Entropy-Scaled Trust Regions for Asynchronous Reinforcement Learning

arXiv:2607. 22186v2 Announce Type: replace Abstract: Asynchronous reinforcement learning (RL) accelerates large language model (LLM) post-training by overlapping rollout generation with policy optimization, but the resulting stale, off-policy data can destabilize optimization and ultimately cause policy collapse.

By Guanqun Zhao, Zijun Xie, Binbin Zheng, Enlei Gong, Jiafeng Lu, Yehan Yang, Aoqi Hu, Zeyu Chen
arXiv AI
6d ago

SCARL: Sequence Confidence-Aligned Reinforcement Learning

SCARL (Sequence Confidence-Aligned Reinforcement Learning) addresses a misalignment between a reinforcement learning policy’s confidence and its reward signal in language-model reasoning. By reshaping each advantage with an alignment gap that reflects the difference between a response’s group-relative confidence and the outcome it certifies, SCARL drives responses with equal advantage toward equal confidence and mitigates entropy collapse. Experiments on Qwen3‑4B‑Base show a 2.4‑point lift in Pass@32 over DAPO and consistent improvements across multiple estimators and backbones while preserving policy entropy.

By Zhenghong Ke, Jingbo Zhou, Hua Wu