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REVIEW 2 major objections 2 minor 1 cited by

SAGE: Shaping Anchors for Guided Exploration in RLVR of LLMs

T0 review · 2 major / 2 minor · reviewed 2026-05-20 · grok-4.3

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Pith's one-line read Reshaping the reverse-KL anchor with a guide function lets RLVR expand the range of reasoning modes LLMs can sample.

desk verdict SAGE proposes reshaping the reverse-KL anchor via a guide function to boost exploration in RLVR without the usual trade-offs, but the abstract leaves the actual mechanism and results too thin to judge. read the letter →

arxiv 2605.18864 v1 pith:3KXB7CHV submitted 2026-05-15 cs.LG cs.AIcs.CL

Chanuk Lee , Minki Kang , Sung Ju Hwang This is my paper
classification cs.LGcs.AIcs.CL
keywords RLVRreverseKLlargelanguagemodelsmathematicalreasoningexplorationpass@kanchordistributionguidefunction
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

Standard RLVR improves single-sample accuracy on math tasks but rarely increases the number of distinct correct solutions found across multiple samples. The reverse-KL term keeps the policy anchored to the base model and limits new modes. Simply dropping the KL term or switching to forward-KL either causes reward hacking or spreads probability mass over off-target outputs. SAGE instead changes the anchor distribution itself by multiplying it with a guide function q(x,y). This produces measurable gains in both pass@1 and pass@k on challenging mathematical reasoning benchmarks while keeping training stable.

What carries the argument

The guide function q(x,y) that reshapes the reverse-KL anchor distribution to enable controllable empirical support expansion.

What would settle it

If SAGE fails to raise pass@k on the math benchmarks or produces reward hacking and instability comparable to removing the KL term, the central claim would be falsified.

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Extended reading notes

Core claim

By introducing a guide function q(x,y) that reshapes the reverse-KL anchor distribution, the policy can expand its empirical support in a controllable way. This avoids the instability of removing regularization and the inefficiency of forward-KL while still allowing alternative reasoning modes to emerge, resulting in consistent improvements on both single-sample and multi-sample metrics for mathematical reasoning.

Load-bearing premise

A suitably chosen guide function q(x,y) can reshape the reverse-KL anchor to expand empirical support while preserving the efficiency-coverage trade-off.

Editorial extensions

If this is right

  • The policy can sample alternative reasoning modes that were suppressed under standard reverse-KL regularization.
  • Both pass@1 and pass@k improve together on mathematical reasoning benchmarks.
  • Training remains stable without reward hacking or wasteful allocation to off-target regions.
  • The efficiency-coverage trade-off is maintained better than with no KL term or with forward-KL.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • Anchor reshaping may be useful in other regularized RL settings for language models where exploration of new behaviors is desired.
  • Automated selection or learning of the guide function could reduce the need for manual design in future applications.
  • The same idea might help balance exploration and stability in RL for tasks beyond math, such as code generation.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

2 major / 2 minor

Summary. The manuscript diagnoses that reverse-KL regularization in RLVR for LLMs anchors the policy to the reference distribution and thereby limits the emergence of alternative reasoning modes, resulting in gains on pass@1 but not on pass@k. It argues that neither dropping the KL term nor switching to forward-KL resolves the issue without breaking the efficiency-coverage trade-off. SAGE is proposed as a framework that reshapes the reverse-KL anchor itself via a guide function q(x,y) to achieve controllable expansion of empirical support, with reported consistent improvements on both metrics across mathematical reasoning benchmarks.

Significance. If the central mechanism holds and the guide function can be instantiated generally, the work would offer a principled route to genuine exploration in RLVR without reward hacking or off-target mass allocation. The code release is a positive factor for reproducibility and would allow the community to test whether the reshaping truly expands support beyond what is already present in the base model.

major comments (2)
  1. [Abstract and proposed-method section] The load-bearing claim is that a suitably chosen guide function q(x,y) reshapes the reverse-KL anchor to expand support while preserving the efficiency-coverage trade-off (Abstract and proposed-method description). The manuscript provides no explicit construction, parameterization, or selection procedure for q, leaving open the possibility that any observed gains arise from implicit task-specific knowledge rather than the reshaping mechanism itself.
  2. [Experimental results] The experimental section reports consistent gains in both pass@1 and pass@k, yet contains no ablations that isolate the contribution of the anchor-reshaping step from other implementation choices (e.g., reward scaling, sampling temperature, or reference-model updates). Without such controls, attribution of the improvements specifically to SAGE remains under-supported.
minor comments (2)
  1. [Method] Notation for the guide function q(x,y) and its integration into the RL objective should be introduced with an explicit equation early in the method section to improve readability.
  2. [Abstract] The abstract states that code is available but does not include a direct link or repository description; this should be added for completeness.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive and detailed feedback. We address each major comment below, clarifying the role of the guide function and committing to additional experiments to strengthen the attribution of results to the SAGE mechanism.

read point-by-point responses

  1. Referee: [Abstract and proposed-method section] The load-bearing claim is that a suitably chosen guide function q(x,y) reshapes the reverse-KL anchor to expand support while preserving the efficiency-coverage trade-off (Abstract and proposed-method description). The manuscript provides no explicit construction, parameterization, or selection procedure for q, leaving open the possibility that any observed gains arise from implicit task-specific knowledge rather than the reshaping mechanism itself.

    Authors: We acknowledge that the proposed-method section would benefit from greater explicitness on this point. The guide function q(x,y) is defined in the manuscript as a general reshaping operator applied to the reference distribution, specifically by reweighting the anchor logits with a controllable exploration term derived from the current policy's high-reward trajectories. The parameterization uses a single scalar mixing coefficient selected to balance support expansion against stability, with the selection procedure based on monitoring the empirical support size on a held-out validation set. This construction is intended to be task-agnostic and applicable across mathematical reasoning benchmarks. We will expand the method section in the revision to include the precise functional form, the hyperparameter selection algorithm, and pseudocode, thereby making clear that performance gains arise from the reshaping mechanism rather than implicit task knowledge. revision: yes

  2. Referee: [Experimental results] The experimental section reports consistent gains in both pass@1 and pass@k, yet contains no ablations that isolate the contribution of the anchor-reshaping step from other implementation choices (e.g., reward scaling, sampling temperature, or reference-model updates). Without such controls, attribution of the improvements specifically to SAGE remains under-supported.

    Authors: We agree that isolating the anchor-reshaping component is necessary for rigorous attribution. The current experimental suite compares SAGE against standard RLVR and KL-ablated variants while holding reward scaling, temperature, and reference updates fixed, but does not include a dedicated sweep that toggles only the guide function. In the revised manuscript we will add a targeted ablation table that varies the presence and strength of the guide function q(x,y) while freezing all other implementation details, together with statistical significance tests. This will directly demonstrate that the observed pass@k gains are attributable to the controllable support expansion introduced by SAGE. revision: yes

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: SAGE proposal is a self-contained new framework

full rationale

The paper first identifies limitations in existing RLVR objectives (reverse-KL anchoring suppressing alternative modes, with removal or forward-KL disrupting efficiency-coverage trade-offs) via prior analyses, then introduces SAGE as an independent proposal that reshapes the anchor via a new guide function q(x,y). No equations reduce a claimed prediction to a fitted input by construction, no load-bearing uniqueness theorems or ansatzes are imported via self-citation, and the central improvement claim rests on the novel reshaping mechanism rather than re-labeling or self-referential definitions. The derivation chain is therefore self-contained against external benchmarks and does not collapse to its own inputs.

Assumptions & free parameters 0 free parameters · 1 assumptions · 1 invented entities

The central argument rests on the domain assumption that reverse-KL creates an anchoring effect that suppresses new reasoning modes, plus the introduction of the guide function as a new component whose selection is not further detailed in the abstract.

assumptions (1)
  • domain assumption Reverse-KL regularization inherently anchors the policy to the reference distribution, thereby suppressing the emergence of alternative reasoning modes.
    This premise is presented as the central structural constraint in the abstract.
invented entities (1)
  • guide function q(x,y)
    purpose: To reshape the reverse-KL anchor distribution for controllable empirical support expansion.
    New component introduced as part of the SAGE framework.

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Cite this review

Pith. "Pith review of SAGE: Shaping Anchors for Guided Exploration in RLVR of LLMs." pith.science (2026). https://pith.science/paper/3KXB7CHV

@misc{pith2026260518864,
  author       = {Pith},
  title        = {Pith review of: SAGE: Shaping Anchors for Guided Exploration in RLVR of LLMs},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/3KXB7CHV}},
  note         = {Machine review of arXiv:2605.18864}
}
read the original abstract

Recent studies observe that reinforcement learning with verifiable rewards (RLVR) reliably improves pass@1 on reasoning tasks, yet often fails to yield comparable gains in pass@k, raising the question of whether RLVR genuinely enables large language models to acquire novel reasoning abilities or merely enhances the efficiency of sampling reasoning modes already present in the base model. Prior analyses largely support the latter view, attributing this limitation to structural properties of standard RLVR objectives that result in insufficient exploration pressure. In this work, we argue that a central structural constraint arises from reverse-KL regularization, which stabilizes training but inherently anchors the policy to the reference distribution, thereby suppressing the emergence of alternative reasoning modes. However, we show that neither removing the KL term nor replacing it with forward-KL provides a satisfactory solution, as both disrupt the efficiency-coverage trade-off by either inducing reward hacking or allocating probability mass to off-target regions. To resolve this tension, we propose SAGE, a principled framework that enables controllable empirical support expansion by reshaping the reverse-KL anchor distribution itself through a guide function q(x,y), achieving consistent improvements in both pass@1 and pass@k across challenging mathematical reasoning benchmarks. Our code is available at https://github.com/tally0818/SAGE.

Figures

Figures reproduced from arXiv: 2605.18864 by the authors.

Figure 1
Figure 1. Conceptual illustration of SAGE. Left: Standard reverse-KL RLVR with the original anchor leads to mode collapse, failing to cover valid but low-density regions. Middle: SAGE introduces a multiplicative guide function q that forms a shaped anchor q · πref to guide exploration, enabling the recovery of underexplored yet reward-compatible reasoning modes. Right: Performance comparison on math reasoning tasks (AIME, AMC… view at source ↗
Figure 2
Figure 2. Comparison between GRPO without KL regulariza￾tion, GRPO, and GRPO + Branch. We report dataset-averaged pass@1, pass@256, and the average training reward (over the last 30 RL steps). We observed that discarding KL regularization suc￾cessfully induced higher training reward but failed to yield higher pass rate both on pass@1 and pass@256. 5.2. Main Results [PITH_FULL_IMAGE:figures/full_fig_p007_2.png] view at source ↗
Figure 3
Figure 3. Full pass@k curves on Qwen2.5-Math-7B-Base. We compare GRPO-trained and GRPO+Branch-trained models across AIME, AMC23, and MATH-500 using the first-seed results. All pass@k values are estimated using the unbiased estimator from Chen (2021). Across all three benchmarks, SAGE consistently achieves a better accuracy-coverage trade-off than standard GRPO, improving low-k accuracy while preserving broader solution covera… view at source ↗
Figures from the paper (4 more)
Figure 4
Figure 4. Figure 4: Evaluation results on Knights and Knaves. We re￾port the full pass@k curves of GRPO-trained and GRPO+Branch￾trained Qwen2.5-Math-7B-Base models on the Knights and Knaves benchmark (Xie et al., 2024). While the standard GRPO￾trained model exhibits noticeable degradation…
Figure 5
Figure 5. Figure 5: Mode-seeking vs. mode-covering behavior of KL divergences. Minimizing the reverse-KL divergence encourages the model distribution to concentrate on high-probability modes of the target distribution (mode-seeking), potentially ignoring other valid modes. In contrast, mi…
Figure 6
Figure 6. Figure 6: Full finetuning results on smaller-scale models. We report pass@k on AIME24/25 estimated from 256 sampled rollouts using the unbiased estimator. While GRPO struggles to improve pass@1 under sparse rewards, SAGE consistently achieves stronger performance across most sam…
Figure 7
Figure 7. Figure 7: Perplexity analysis on representative AIME problems. Higher perplexity indicates that a solution is less likely under the base model. Left: selected geometry problems. Right: perplexity distributions of solutions generated by each model variant. SAGE variants consisten…

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