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arxiv: 2509.20712 · v5 · submitted 2025-09-25 · 💻 cs.LG · cs.CL

CE-GPPO: Coordinating Entropy via Gradient-Preserving Clipping Policy Optimization in Reinforcement Learning

Pith reviewed 2026-05-18 15:02 UTC · model grok-4.3

classification 💻 cs.LG cs.CL
keywords reinforcement learningpolicy optimizationentropy dynamicsclipping mechanismlarge language modelsexploration exploitationmathematical reasoning
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The pith

CE-GPPO reintroduces bounded gradients from clipped tokens to stabilize entropy and improve the exploration-exploitation balance in RL for LLMs.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper establishes that standard clipping in PPO discards gradient signals from low-probability tokens, which disrupts entropy dynamics and harms the balance between exploration and exploitation. CE-GPPO addresses this by gently reintroducing those gradients in a controlled way while keeping changes to the native PPO algorithm minimal. A sympathetic reader would care because entropy management is central to effective RL fine-tuning of language models on reasoning tasks, and the method shows consistent gains across model scales on mathematical benchmarks along with theoretical support for reduced instability.

Core claim

Analysis of entropy dynamics shows clipped tokens play a critical overlooked role in regulation. CE-GPPO reintroduces their gradients in a gentle and bounded manner by controlling magnitude outside the clipping interval, achieving a better exploration-exploitation trade-off. Theoretical justification and experiments on reasoning benchmarks confirm it mitigates entropy instability while outperforming strong baselines.

What carries the argument

Gradient-preserving clipping, which reintroduces gradients from tokens outside the clipping interval in a bounded manner to coordinate entropy evolution without altering the core PPO update.

Load-bearing premise

That reintroducing gradients from clipped tokens in a bounded manner will stabilize entropy evolution without creating new training instabilities or performance drops.

What would settle it

Run CE-GPPO and standard PPO on the same mathematical reasoning benchmarks and measure whether entropy variance decreases and final performance improves without new divergence or regression.

Figures

Figures reproduced from arXiv: 2509.20712 by Fuzheng Zhang, Guorui Zhou, Kun Gai, Leiyu Pan, Minxuan Lv, Wenping Hu, Yuntao Li, Zhenpeng Su.

Figure 1
Figure 1. Figure 1: Left: Importance sampling distribution of tokens with different probabilities. Based on the distribution, all tokens can be categorized into four types: PA&HP, NA&LP, PA&LP and NA&HP. Center: The effect of the four token types on entropy dynamics. The two categories shown at the top contribute to entropy reduction, while those at the bottom contribute to entropy increase. Green check marks indicate tokens … view at source ↗
Figure 2
Figure 2. Figure 2: Based on DeepSeek-R1-Distill-Qwen-7B, a comparison of GRPO, DAPO, and GPPO in terms of entropy dynamics and AIME25 benchmark accuracy. potential data contamination, the dataset has been further processed with 9-gram deduplication against the evaluation benchmarks. Training We conducted training with CE-GPPO on two model sizes, DeepSeek-R1-Distill-Qwen￾1.5B and DeepSeek-R1-Distill-Qwen-7B. The max￾imum trai… view at source ↗
Figure 3
Figure 3. Figure 3: Entropy dynamics and benchmark accuracy under different β1/β2 configurations. key finding that the choice of β1 and β2 directly governs the evolution of entropy. The underlying mechanism is that: • A larger β1 amplifies gradients beyond the left clip boundary (mainly from NA&LP tokens). These gradients strengthen high-probability to￾kens, accelerating exploitation and thus causing entropy to collapse quick… view at source ↗
Figure 4
Figure 4. Figure 4: Comparison of KL divergence and gradient [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Comparison of CE-GPPO with other en￾tropy collapse mitigation strategies. Native GRPO denotes the baseline without any mitigation strategy. α = 0.001/0.003 indicate the addition of an entropy loss term to the Native GRPO baseline, where α repre￾sents the entropy loss coefficient. DAPO refers to apply￾ing the Clip Higher strategy on Native GRPO baseline. balance between exploration and exploitation. • Compa… view at source ↗
Figure 6
Figure 6. Figure 6: Entropy dynamics and benchmark accuracy under different β1/β2 configurations. For β1 = 0/β2 = 1, the setting is maintained consistently across 0–1000 steps. For β1 = 0/β2 = 1 → β1 = 0.5/β2 = 1 configuration, the transition occurs at step 585. A Appendix A.1 The Role of Entropy at Different Stages of Training We further investigate the role of entropy at differ￾ent stages of training. The results show that … view at source ↗
read the original abstract

Reinforcement learning (RL) has become a powerful paradigm for optimizing large language models (LLMs) to handle complex reasoning tasks. A core challenge in this process lies in managing policy entropy, which reflects the balance between exploration and exploitation during training. Existing methods, such as proximal policy optimization (PPO) and its variants, discard valuable gradient signals from low-probability tokens due to the clipping mechanism. We systematically analyze the entropy dynamics and reveal that these clipped tokens play a critical yet overlooked role in regulating entropy evolution. We propose \textbf{C}oordinating \textbf{E}ntropy via \textbf{G}radient-\textbf{P}reserving \textbf{P}olicy \textbf{O}ptimization (CE-GPPO), a novel algorithm that reintroduces gradients from clipped tokens in native PPO in a gentle and bounded manner. By controlling the magnitude of gradients from tokens outside the clipping interval, CE-GPPO is able to achieve an exploration-exploitation trade-off. We provide theoretical justification and empirical evidence showing that CE-GPPO effectively mitigates entropy instability. Extensive experiments on mathematical reasoning benchmarks show that CE-GPPO consistently outperforms strong baselines across different model scales.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper introduces CE-GPPO as an extension to standard PPO for RL-based optimization of LLMs on reasoning tasks. It claims that clipped tokens in PPO's surrogate objective play an overlooked role in entropy dynamics; the proposed method reintroduces their gradients in a bounded manner to stabilize entropy, improve the exploration-exploitation trade-off, and yield better performance. The manuscript provides a theoretical analysis of the modified gradient and reports empirical gains on mathematical reasoning benchmarks across model scales.

Significance. If the bounded reintroduction of clipped-token gradients can be shown to preserve PPO's trust-region guarantees while demonstrably stabilizing entropy, the approach would offer a lightweight, interpretable improvement to existing RLHF pipelines for reasoning models. The empirical results on standard math benchmarks, if reproducible and properly controlled, would constitute a practical contribution even if the theoretical novelty is incremental.

major comments (2)
  1. [Theoretical justification] Theoretical justification section: the derivation of the modified gradient term for tokens outside the clipping interval does not explicitly bound the total KL divergence or demonstrate that the advantage-weighted contribution from out-of-clip tokens remains dominated by the original clipped surrogate. Without this step, it is unclear whether the entropy-stability argument preserves the monotonic-improvement property of the PPO surrogate.
  2. [Empirical evaluation] §4 (or equivalent empirical section), Table or Figure reporting main results: the manuscript does not detail the exact clipping threshold, the gradient-magnitude bound hyperparameter, or the data-exclusion rules used in the entropy-dynamics plots; these omissions make it impossible to verify that the reported entropy stabilization is not an artifact of the chosen bound or of selective token filtering.
minor comments (2)
  1. [Method] Notation for the bounded gradient term should be introduced with an explicit equation number and contrasted directly with the standard PPO clipping indicator.
  2. [Abstract and introduction] The abstract states 'theoretical justification' but the main text should include a short lemma or corollary that isolates the entropy-control effect from the performance improvement.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive feedback and the recommendation for major revision. We address each major comment point by point below, indicating the specific revisions we will incorporate to strengthen the manuscript.

read point-by-point responses
  1. Referee: [Theoretical justification] Theoretical justification section: the derivation of the modified gradient term for tokens outside the clipping interval does not explicitly bound the total KL divergence or demonstrate that the advantage-weighted contribution from out-of-clip tokens remains dominated by the original clipped surrogate. Without this step, it is unclear whether the entropy-stability argument preserves the monotonic-improvement property of the PPO surrogate.

    Authors: We thank the referee for identifying this gap in the theoretical presentation. Our current derivation bounds the per-token gradient contribution from out-of-clip tokens via a magnitude hyperparameter, which directly limits their influence on the policy update and thereby stabilizes entropy. To make the connection to PPO's trust-region guarantees explicit, we will revise the theoretical justification section to include a formal bound on the additional KL divergence induced by these terms and demonstrate that their advantage-weighted contribution remains strictly dominated by the clipped surrogate terms. This addition will confirm that the monotonic-improvement property is preserved under the bounded modification. revision: yes

  2. Referee: [Empirical evaluation] §4 (or equivalent empirical section), Table or Figure reporting main results: the manuscript does not detail the exact clipping threshold, the gradient-magnitude bound hyperparameter, or the data-exclusion rules used in the entropy-dynamics plots; these omissions make it impossible to verify that the reported entropy stabilization is not an artifact of the chosen bound or of selective token filtering.

    Authors: We agree that these details are necessary for full reproducibility and to rule out potential artifacts. In the revised manuscript we will explicitly report the clipping threshold (ε = 0.2), the gradient-magnitude bound hyperparameter (λ = 0.05), and the precise token-filtering criteria applied when generating the entropy-dynamics plots. These additions will allow independent verification that the observed stabilization arises from the proposed mechanism rather than from hyperparameter choice or selective data handling. revision: yes

Circularity Check

0 steps flagged

No significant circularity in derivation chain

full rationale

The paper presents CE-GPPO as an extension of standard PPO that adds a bounded gradient contribution from clipped tokens to stabilize entropy. The abstract and provided context describe an analysis of entropy dynamics followed by a proposed modification with theoretical justification and empirical validation on reasoning benchmarks. No equations or steps are shown that reduce the claimed entropy control or performance gains to a fitted parameter renamed as prediction, a self-referential definition, or a load-bearing self-citation whose validity depends on the current work. The derivation appears self-contained against external PPO baselines and benchmark results.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The method rests on the domain assumption that entropy dynamics are primarily driven by gradients from out-of-clip tokens and introduces at least one tunable magnitude control for those gradients.

free parameters (1)
  • gradient magnitude bound for clipped tokens
    The paper states that CE-GPPO controls the magnitude of gradients from tokens outside the clipping interval, implying a tunable or chosen bound parameter.
axioms (1)
  • domain assumption Clipped tokens play a critical yet overlooked role in regulating entropy evolution
    This premise is stated as the result of the systematic analysis of entropy dynamics in existing PPO variants.

pith-pipeline@v0.9.0 · 5771 in / 1148 out tokens · 42772 ms · 2026-05-18T15:02:48.492017+00:00 · methodology

discussion (0)

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Forward citations

Cited by 7 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Entropy Polarity in Reinforcement Fine-Tuning: Direction, Asymmetry, and Control

    cs.LG 2026-05 unverdicted novelty 7.0

    Entropy polarity from a first-order entropy change approximation enables Polarity-Aware Policy Optimization (PAPO) that preserves complementary polarity branches and outperforms baselines on math and agentic RL fine-t...

  2. Entropy Polarity in Reinforcement Fine-Tuning: Direction, Asymmetry, and Control

    cs.LG 2026-05 unverdicted novelty 6.0

    Entropy polarity is a signed token-level quantity derived from a first-order approximation of entropy change that predicts whether RL updates expand or contract policy entropy in LLM fine-tuning, revealing an asymmetr...

  3. Flexible Entropy Control in RLVR with a Gradient-Preserving Perspective

    cs.LG 2026-02 unverdicted novelty 6.0

    Dynamic clipping strategies based on importance sampling regions enable precise entropy management in RLVR, mitigating collapse and improving benchmark performance.

  4. Entropy Ratio Clipping as a Soft Global Constraint for Stable Reinforcement Learning

    cs.LG 2025-12 unverdicted novelty 6.0

    Entropy Ratio Clipping introduces a global entropy-ratio constraint that stabilizes RL policy updates in LLM post-training beyond local PPO clipping.

  5. Revisiting Entropy in Reinforcement Learning for Large Reasoning Models

    cs.CL 2025-11 unverdicted novelty 6.0

    Tokens with positive advantages primarily drive entropy collapse in RLVR training of LLMs, and reweighting their loss contributions regulates entropy while maintaining competitive performance.

  6. OGER: A Robust Offline-Guided Exploration Reward for Hybrid Reinforcement Learning

    cs.AI 2026-04 unverdicted novelty 5.0

    OGER adds an auxiliary exploration reward built from offline trajectories and model entropy to hybrid RL training, yielding gains on math reasoning benchmarks and out-of-domain generalization.

  7. Targeted Exploration via Unified Entropy Control for Reinforcement Learning

    cs.AI 2026-04 unverdicted novelty 5.0

    UEC-RL improves RL reasoning performance in LLMs and VLMs by activating exploration on hard prompts and stabilizing entropy, delivering a 37.9% relative gain over GRPO on Geometry3K.

Reference graph

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