做RLHF或推理模型训练的团队，终于有了一个能精准分配token级信用的方法——DelTA解决了高频格式token淹没关键信号的问题，数学和代码任务上效果显著，值得在自家模型上试试。
DelTA提出了一种新方法，解决强化学习从可验证奖励（RLVR）中训练大语言模型时，token级信用分配不准确的问题。研究发现，标准RLVR更新中，高频格式token会主导梯度方向，掩盖真正区分高/低奖励的关键token。DelTA通过估计token系数，放大判别性方向、抑制共享模式，使更新更聚焦于推理关键步骤。在7个数学基准上，DelTA在Qwen3-8B和14B上分别平均提升3.26和2.62分，代码生成和跨领域任务也验证了其泛化能力。
DelTA: Discriminative Token Credit Assignment for Reinforcement Learning from Verifiable Rewards
Reinforcement learning from verifiable rewards (RLVR) has emerged as a central technique for improving the reasoning capabilities of large language models. Despite its effectiveness, how response-level rewards translate into token-level probability changes remains poorly understood. We introduce a discriminator view of RLVR updates, showing that the policy-gradient update direction implicitly acts as a linear discriminator over token-gradient vectors and thereby determines which token probabilities are increased or decreased during learning. Under standard sequence-level RLVR, this discriminator is constructed from positive- and negative-side centroids formed by advantage-weighted averaging of token-gradient vectors. However, such centroid construction can be dominated by shared high-frequency patterns, such as formatting tokens, diluting sparse yet discriminative directions that better distinguish high-reward responses from low-reward ones. To address this limitation, we propose $\textbf{DelTA}$, a discriminative token credit assignment method that estimates token coefficients to amplify side-specific token-gradient directions and downweight shared or weakly discriminative ones. These coefficients reweight a self-normalized RLVR surrogate, making the effective side-wise centroids more contrastive and thereby reshaping the RLVR update direction. On seven mathematical benchmarks, DelTA outperforms the strongest same-scale baselines by 3.26 and 2.62 average points on Qwen3-8B-Base and Qwen3-14B-Base, respectively. Additional results on code generation, a different backbone, and out-of-domain evaluations further demonstrate the generalization ability of DelTA.