STARE解决了GRPO训练中策略熵崩溃的老问题，在AIME数学竞赛上比DAPO高4-8个点，代码也开源了，搞RL训练的同学可以试试。
STARE针对GRPO等强化学习训练中策略熵崩溃问题，提出令牌级信用分配纠偏方法。通过惊讶度分位数识别熵关键令牌子集，选择性重加权其有效优势，并引入目标熵闭环门控实现稳定熵调节。在1.5B至32B规模模型及短CoT、长CoT、多轮工具使用三类任务中，STARE可维持数千步稳定训练。在AIME24和AIME25上，STARE准确率较DAPO等基线提升4%-8%，反射令牌和响应长度同步增长，表明探索-利用平衡得到改善。代码已开源。
STARE: Surprisal-Guided Token-Level Advantage Reweighting for Policy Entropy Stability
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. We conduct a first-order gradient analysis of token-level entropy dynamics under GRPO and identify a token-level credit assignment mismatch: the per-token entropy variation decomposes into the product of the trajectory-level advantage and an entropy sensitivity function over the next-token distribution, yielding an advantage-surprisal four-quadrant structure and a near-criticality property. Motivated by it, we propose STARE (Surprisal-guided Token-level Advantage Reweighting for policy Entropy stability), which identifies entropy-critical token subsets via batch-internal surprisal quantiles, selectively reweights their effective advantages, and incorporates a target-entropy closed-loop gate for stable entropy regulation. Across model scales from 1.5B to 32B and three task families (Short CoT, Long CoT, and Multi-Turn Tool Use), STARE sustains stable RL training over thousands of steps while maintaining policy entropy within the target band. On AIME24 and AIME25, STARE outperforms DAPO and other competitive baselines by 4%-8% in average accuracy, with reflection tokens and response length growing in tandem, indicating sustained exploration-exploitation balance that further unlocks RL training potential.Code is available at https://github.com/hp-luo/STARE.