REVIEW 1 major objections 7 minor 27 references
Reviewed by Pith at T0; open to challenge.
T0 means a machine referee read the full paper against a public rubric. The mark states how deep the mechanical check went, never who wrote it. the ladder, T0–T4 →
T0 review · glm-5.2
Thinking can make AI less factual — now there's a fix
2026-07-08 22:08 UTC pith:GJJTWWJP
load-bearing objection MARGO mixes thinking and non-thinking rollouts in the same GRPO group — a clean, genuinely new mechanism for a real problem. The math is correct, the method is lightweight, and math ability is preserved. The main concern is evaluation validity: one judge model (Qwen3-32B) is used for data selection, training rewards, and all test evaluation, with no error bars. Still worth a serious referee. the 1 major comments →
Mitigating Factual Hallucination in Large Reasoning Models via Mixed-Mode Advantage Regularization
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The paper's central contribution is the decomposition of mixed-mode advantage into two terms: a within-mode advantage (how good this thinking trajectory is compared to other thinking trajectories) and a residual-value adjustment (whether thinking as a whole helps or hurts factuality for this question, measured against the non-thinking baseline). This second term is absent in standard GRPO, which only compares thinking trajectories to each other. By including non-thinking rollouts in the same group, MARGO automatically suppresses thinking that corrupts correct direct answers while preserving thinking that recovers missing knowledge, without requiring a separate classifier or hand-crafted mode
What carries the argument
MARGO constructs mixed rollout groups containing both thinking and non-thinking trajectories for each question, then applies standard GRPO advantage normalization across the mixed group. The thinking ratio α controls the proportion of thinking vs non-thinking samples (set to 0.75 in experiments, meaning 6 thinking and 2 non-thinking rollouts per group).
Load-bearing premise
The same model (Qwen3-32B) serves as both the training reward signal and the evaluation judge, using the same prompt. If this judge has systematic biases toward certain answer formats or phrasings that MARGO's outputs happen to match, the reported gains could be partially artifactual rather than reflecting genuine factual improvement.
What would settle it
Run MARGO with a different judge model for evaluation than for training, or add human evaluation on a sample of outputs, and check whether the gains persist.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This paper introduces MARGO, a mixed-mode GRPO variant that places thinking and non-thinking trajectories in the same rollout group for factuality-oriented QA. The core idea is that non-thinking responses serve as same-model references in advantage estimation, so that thinking trajectories are penalized when they degrade factuality relative to direct answering. The advantage decomposition (Proposition 1, Appendix A) shows that the mixed-mode advantage of a thinking trajectory decomposes into a within-thinking advantage plus a residual-value adjustment proportional to the thinking/non-thinking reward gap. Experiments on Qwen3-4B and Qwen3-8B across six factuality QA benchmarks show consistent improvements over fixed-mode and adaptive baselines, while mathematical reasoning ability is preserved. The transition analysis (Tables 1, 6–8) documenting thinking-induced hallucination is a useful empirical contribution.
Significance. The paper addresses a real and timely problem: thinking-induced hallucination in large reasoning models on factuality tasks. The mixed-mode advantage decomposition (Proposition 1) is a clean, correct mathematical result that directly motivates the method. The transition analysis across multiple benchmarks and model scales (Tables 1, 6–8, including the GSM8K contrast in Table 8) provides solid empirical grounding for the phenomenon. The data selection ablation (Table 3) and the transition-ratio analysis (Figure 2a–b) are well-designed controls that isolate the contribution of mixed-mode regularization from RL or data selection alone. The method is simple to implement and the experimental setup is reasonably comprehensive.
major comments (1)
- §4.1, Appendix B, Appendix C.1: The same judge model (Qwen3-32B) with the same prompt is used for (a) training data filtering (Eqs. 25–32), (b) reward computation during RL training (Eq. 13), and (c) all six test-benchmark evaluations. This creates a measurement loop: if Qwen3-32B has systematic biases in semantic matching (e.g., favoring certain answer formats, lengths, or phrasings), MARGO could learn to exploit these during RL training, and the same biases would inflate test scores. The paper acknowledges that the judge performs ground-truth-conditioned matching rather than open-ended verification (Appendix B), which mitigates but does not eliminate this concern. The SimpleQA-V column in Table 2 is particularly striking: on Qwen3-4B, MARGO jumps from 4.10% (FixedThink) to 10.00% (+5.90 absolute, +144% relative), while FixedThink+RL stays flat at 4.10%. This is more than double the per
minor comments (7)
- Table 2: No error bars, confidence intervals, or significance tests are reported for any benchmark. Given that several gains are in the 1–3% range (e.g., TriviaQA 4B: +1.68% over FixedThink+RL), it is difficult to assess whether these are within sampling noise. Adding bootstrap confidence intervals or at least reporting results over multiple random seeds would strengthen the claims.
- §4.1: The evaluation uses temperature 0.6 for thinking and 0.7 for non-thinking mode. It would help to clarify whether the reported numbers are single-run or averaged over multiple samples, and whether the same decoding settings were used for all baselines.
- Table 3 (data selection ablation) is only reported on Qwen3-4B. Including the 8B ablation would make the data-selection claim more robust.
- Figure 2a–b: The y-axis labels and bar values are somewhat hard to read. Consider using a table format or increasing font size.
- §C.1, Eqs. 29–30: The threshold for thinking-favored examples on Qwen3-4B requires Δ(x) ≥ 1.0 and S_T(x) ≥ 1.0. Since S_T is computed from N=6 samples, S_T(x) ≥ 1.0 means all 6 thinking samples are correct. This is a very strict threshold; it would help to report how many examples satisfy each condition.
- The paper would benefit from a brief discussion of how α (the thinking ratio) was chosen. Only α=0.75 is tested; a small ablation over α values would clarify sensitivity.
- References: Several entries have incomplete formatting (e.g., 'Guibin Zhang et al.' missing venue/year; 'Pingzhi Li et al.' missing year).
Simulated Author's Rebuttal
We thank the referee for the careful and constructive review. The referee identifies a valid concern about the measurement loop created by using the same judge model (Qwen3-32B) for training data filtering, RL reward computation, and test evaluation. We agree this is a legitimate methodological concern and will address it in revision by adding an independent evaluation judge and discussing the limitations of the shared-judge design. The core contributions—the thinking-induced hallucination phenomenon, the advantage decomposition, and the mixed-mode regularization mechanism—are independent of the specific judge used, but we acknowledge the referee's point that the current evaluation setup does not fully rule out judge-bias exploitation.
read point-by-point responses
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Referee: §4.1, Appendix B, Appendix C.1: The same judge model (Qwen3-32B) with the same prompt is used for (a) training data filtering, (b) reward computation during RL training, and (c) all six test-benchmark evaluations. This creates a measurement loop where MARGO could learn to exploit Qwen3-32B's systematic biases during RL training, and the same biases would inflate test scores. The SimpleQA-V result on Qwen3-4B (4.10% to 10.00%, +144% relative) is particularly striking.
Authors: We agree with the referee that using the same judge model for training data filtering, RL reward computation, and test evaluation creates a potential measurement loop. This is a legitimate methodological concern. We will address it through the following revisions: (1) We will add an independent evaluation using a different judge model (e.g., GPT-4o or Llama-3.3-70B) on at least a subset of benchmarks to verify that MARGO's improvements are not artifacts of Qwen3-32B's biases. (2) We will add an explicit discussion of this limitation in the paper, acknowledging the shared-judge concern and explaining why ground-truth-conditioned semantic matching (as opposed to open-ended verification) mitigates—but does not eliminate—the risk. (3) Regarding the SimpleQA-V jump specifically: we note that FixedThink+RL, which uses the same judge for reward computation and the same training data, does NOT show this gain (staying at 4.10%), which suggests the improvement is attributable to the mixed-mode advantage mechanism rather than simple judge exploitation. If MARGO were merely learning to exploit judge biases, we would expect FixedThink+RL to benefit similarly since it shares the same reward signal. That said, we acknowledge this argument is not fully conclusive without an independent judge, and we will provide the cross-judge evaluation to properly address the concern. revision: yes
Circularity Check
No circularity found: advantage decomposition is a genuine algebraic identity; judge reuse is a measurement concern, not a circularity.
full rationale
The paper's central theoretical result (Proposition 1, Eq. 19/22) is a straightforward algebraic identity: substituting the mixed-baseline definition μ_mix = αμ_T + (1-α)μ_N into R(y_T) - μ_mix and rearranging yields the decomposition [R(y_T) - μ_T] + (1-α)Δ_res. This is not circular—it is a valid mathematical derivation from stated definitions. The training data filtering (Appendix C.1, Eqs. 25-32) selects examples with large thinking/non-thinking factuality gaps, which is a legitimate data curation choice, not a fitted input renamed as prediction. The experimental results compare MARGO against multiple baselines (FixedThink+RL, FixedNoThink+RL, AdaptiveRL, etc.) trained on the same data, isolating the mixed-mode advantage mechanism from RL alone. The reader's concern about Qwen3-32B serving as judge for both training rewards and evaluation is a valid measurement-validity concern (potential systematic bias inflating results), but it is not circularity in the sense of a derivation reducing to its inputs by construction. The judge performs ground-truth-conditioned semantic matching, not open-ended factual verification, and the same judge is applied to all baselines equally. No self-citation chain is load-bearing for the central claim. The paper is self-contained against external benchmarks.
Axiom & Free-Parameter Ledger
free parameters (7)
- α (thinking ratio in rollout group) =
0.75
- Learning rate =
1e-6
- KL loss coefficient =
0.001
- Data selection thresholds (Qwen3-4B) =
Δ≤-0.7, SN≥0.7 / Δ≥1.0, ST≥1.0
- Data selection thresholds (Qwen3-8B) =
Δ≤-0.5, SN≥0.5 / Δ≥0.7, ST≥0.7
- Format reward bonus =
0.05
- Correctness reward =
+1/-1
axioms (4)
- standard math GRPO with group-relative advantage normalization is a valid RL training procedure for LLMs
- domain assumption Qwen3-32B can reliably judge semantic equivalence between model predictions and ground-truth answers in factual QA
- domain assumption The thinking/non-thinking mode distinction (via prompting template) captures a meaningful behavioral difference in the model's factual tendency
- ad hoc to paper Training examples with large thinking/non-thinking factuality gaps are more informative for mixed-mode optimization than random examples
read the original abstract
Large reasoning models (LRMs) improve language model capabilities by generating explicit thinking traces before final answers. In factuality-oriented question answering (QA), such thinking often improves overall performance by helping the model recover relevant knowledge and refine its answers. However, we find that this benefit is not uniform at the instance level: explicit thinking can also overturn correct non-thinking answers and lead to factual drift. We refer to this failure mode as \emph{thinking-induced hallucination}. To explain this phenomenon, we formulate explicit thinking in factuality QA as a thinking residual over the model's direct-answer tendency, which can either recover missing knowledge or introduce unsupported associations. Based on this formulation, we propose MARGO, \underline{\textit{M}}ixed-Mode \underline{\textit{A}}dvantage \underline{\textit{R}}egularization for \underline{\textit{G}}rounded \underline{\textit{O}}ptimization, a reinforcement learning framework that uses non-thinking rollouts as same-model references in advantage estimation. By constructing mixed-mode rollout groups with both thinking and non-thinking trajectories, MARGO evaluates whether explicit thinking adds factual value beyond direct answering, thereby suppressing hallucination-prone thinking while preserving beneficial thinking behaviors. Experiments across multiple factuality-oriented QA benchmarks demonstrate that MARGO improves factual reliability over strong baselines, while evaluations on mathematical benchmarks show that it preserves general reasoning ability.
Figures
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12 Limitations This work focuses on improving the factual reliability of LRMs in factuality-oriented QA. While our experiments cover multiple benchmarks and model scales, future work can further explore the applicability of mixed-mode advantage regularization to broader scenarios, such as open-ended generation, multi-turn interaction, retrieval-augmented ...
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,→ ,→ ``` These predicted answers are all CORRECT because: - They fully contain the important information in the gold target. - They do not contain any information that contradicts the gold target. - Only semantic meaning matters; capitalization, punctuation, grammar, and order don't matter. - Hedging and guessing are permissible, provided that the gold t...
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Specifically, we report Mean@16 and Pass@16 on AMC23, AIME24, and AIME25 for both Qwen3-4B and Qwen3-8B. Compared with 17 Method AMC23 AIME24 AIME25 AverageMean@16 Pass@16 Mean@16 Pass@16 Mean@16 Pass@16 Qwen3-4B FixedN oT hink 67.0 92.5 23.3 53.3 21.7 46.7 37.3 FixedT hink 95.8 100.0 73.8 83.3 64.4 86.7 78.0 MARGO96.2100.073.890.065.490.078.5 Qwen3-8B Fi...
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discussion (0)
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