REVIEW 5 major objections 6 minor 4 cited by
Revisiting Overthinking in Long Chain-of-Thought from the Perspective of Self-Doubt
T0 review · 5 major / 6 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read This paper shows that self-doubt, not length alone, drives overthinking in reasoning LLMs, and that a one-line prompt asking the model to check input validity before answering cuts token use by about 37% while keeping or improving accuracy.
desk verdict Useful prompt-based token reduction with a plausible but unvalidated self-doubt mechanism; the causal claim needs a be-concise control and a human-checked judge before it supports the framing. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the three-way classification of a generated reasoning path into self-doubt, overthinking without self-doubt, and non-overthinking, assigned by a judge model to the second half of each response split at paragraph boundaries. The intervention itself is a prompt template: before reasoning deeply, the model must check whether all necessary information is available; if anything is missing or ambiguous, it must say so first, otherwise it should answer with the minimum number of tokens required. This prompt is what carries the causal claim, because the paper attributes the length reduction to the reduction in re-verification rather than to the brevity instruction alone.
What would settle it
A decisive experiment would be a brevity-only control: replace the prompt's validity-check clause with a neutral sentence while keeping 'minimum number of tokens.' If the length reduction survives, the paper's claim that reduced self-doubt causes the saving is unsupported. A second check would compare the judge's self-doubt labels to human labels on a random sample of 200 responses per dataset.
Extended reading notes
Core claim
The central discovery is that self-doubt is a measurable, dominant component of overthinking in reasoning LLMs, and that it can be reduced by a prompt that makes the model critically evaluate the input before committing to a long chain of thought. The paper supports this with a three-way classification of responses (self-doubt, overthinking without self-doubt, non-overthinking) and shows that self-doubt is especially prevalent on harder problems, reaching 59.5% on Math-500. The proposed prompt consistently reduces response length by roughly a third, maintains or improves accuracy on GSM8K, GSM8K-Zero, and Math-500, and improves abstain rates on four missing-premise datasets. The authors interpret the result as evidence that apparent sycophancy toward the user input causes the model to keep checking its own work.
Load-bearing premise
The load-bearing premise is that the automated judge, applied to the second half of each response after splitting at paragraph breaks, correctly identifies self-doubt; the paper reports no human agreement check.
Editorial extensions
If this is right
- On well-defined math tasks, the prompt cuts response length by about 37% on average across the four tested reasoning models while keeping accuracy roughly flat or better (e.g., +16.7 and +14.7 points on GSM8K-Zero for the 32B and 70B DeepSeek models).
- On missing-premise datasets, the prompt raises abstain rates by up to nearly 40 percentage points and cuts token use by more than half on most settings, so models stop guessing when the question is under-specified.
- The number of reasoning steps drops on all three math datasets, indicating the intervention changes the reasoning process itself, not just the wording of the final response.
- Because the method is a zero-shot prompt addition, it can be deployed on existing reasoning models without fine-tuning or architectural changes.
Reading between the lines
- Not tested here: a brevity-only control prompt (minimum tokens without the validity check) would isolate whether the effect comes from reducing self-doubt or just from instructing brevity.
- The paper's math-only scope leaves open whether the same prompt curbs self-doubt in commonsense reasoning, planning, or multimodal tasks; a transfer test would settle it.
- If the judge labels are correct, training-time rewards could penalize re-verification of already-correct steps, making the efficiency gain a permanent model property rather than a prompt effect.
- Human annotation of a small sample of classified responses would show whether 'self-doubt' is a stable, recognizable behavior across models or a byproduct of the paragraph-splitting heuristic.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper quantifies overthinking in long chain-of-thought (CoT) reasoning for reasoning LLMs by labeling reasoning paths as self-doubt, overthinking without self-doubt, or non-overthinking using Qwen2.5-72B-Instruct as an LLM judge. It reports that self-doubt is a major component of overthinking (e.g., 59.5% on MATH-500 for DeepSeek-R1-Distill-Qwen-32B) and proposes a simple prompting intervention: ask the model to check whether the input question has all necessary information, then answer with the minimum number of tokens. Experiments on GSM8K, GSM8K-Zero, MATH-500, and four missing-premise datasets across four RLLMs show large response-length reductions and improved abstain rates, with an average length reduction of 37.1% and an average accuracy change of +3.6% on well-defined tasks.
Significance. If the mechanistic claims were established, the paper would be practically valuable: a one-line prompt that reduces token usage by about one-third while preserving accuracy on math tasks and sharply improving missing-premise abstention could reduce inference cost in deployed RLLMs. The paper is also useful as a reproducible starting point because it specifies models, datasets, prompt templates, and judge templates. However, the central causal claim—that self-doubt drives overthinking and that the prompt reduces overthinking by reducing self-doubt—currently rests on an unvalidated LLM-based metric and is confounded by the prompt's explicit token-minimization instruction. The practical length-reduction result is credible, but the mechanistic interpretation and the "significant improvement" language are not yet supported.
major comments (5)
- [Section 2 / Appendix A, Table 5] The self-doubt metric is computed by Qwen2.5-72B-Instruct on only the second half of each response split by "\n\n", with no human validation, inter-annotator agreement, or alternative metric reported. The Limitations section concedes that the judge "may misunderstand nuanced reasoning patterns or miss subtle verification steps." Because Figure 1 and Table 4 are the only quantitative evidence that self-doubt is a major driver of overthinking and that the prompt reduces self-doubt, this unvalidated measurement is load-bearing. Please report human agreement on a sample and validate the paragraph-splitting heuristic.
- [Section 3 / Table 2] The treatment prompt explicitly instructs the model to "answer it with the minimum number of tokens required." The large length reductions in Tables 1 and 3, and the drop in self-doubt in Table 4 as judged by a rubric that flags "unnecessarily long reasoning," can be explained purely as compliance with a brevity instruction. A control with a conciseness-only prompt (no premise-validity check) is needed to attribute the effect to the critique step or to reduced self-doubt rather than to the explicit token-minimization directive.
- [Section 5 / Table 1] The abstract and Section 5 claim "significant improvements across nearly all datasets," but no significance tests are reported and several accuracy numbers decrease (e.g., DS-14B MATH-500 92.8 to 92.2, DS-70B MATH-500 92.4 to 91.6, Qwen3-32B MATH-500 97.2 to 96.8). The term "significant" should be supported by paired tests or confidence intervals, or the claim should be revised to reflect mixed accuracy changes with consistent length reduction.
- [Section 5 / Table 3] The missing-premise abstain-rate gains are partly a direct effect of the instruction "If any key data is missing or ambiguous, explicitly state that first," so the large abstain-rate improvements do not by themselves demonstrate improved critique ability or reduced self-doubt. Please include a control that gives the same missing-premise clue without the conciseness instruction, and report non-abstaining answer quality so that the MiP results are not evaluated only on the instructed behavior.
- [Section 3 / Section 6, Table 4] The causal narrative that self-doubt drives overthinking and that the prompt works by reducing self-doubt is not directly tested. Table 4 shows the self-doubt ratio increases on GSM8K (5.9 to 17.2), which the paper attributes to "early verification" without supporting evidence; this inconsistency, together with the lack of any manipulation of model confidence or user-deference, weakens the mechanistic claim. At minimum, report per-dataset examples and a confidence-related metric that is not defined by the same brevity criterion as the intervention.
minor comments (6)
- [Section 4 / Section 5] Section 5 contains "Results on 1" instead of "Table 1," and Section 4 has "statistic metric" instead of "statistical metric."
- [Figure 1] The caption misspells "Deepseek" and "Non-Overtinking."
- [Section 3 / Table 2] The text describes a two-stage process ("first prompt the model... then instruct"), but Table 2 shows a single user message containing both instructions; please clarify whether the intervention is one stage or two.
- [Table 4] The table does not define the denominator or report confidence intervals for the self-doubt ratio; specify whether it is computed over all examples or only over overthinking examples.
- [Appendix A] Decoding details for the Qwen2.5-72B-Instruct judge (temperature, number of samples, version) are omitted; since the judge is a core measurement instrument, these details should be provided for reproducibility.
- [Table 6] The baseline and "Ours" responses are nearly identical in their opening sentences; please indicate whether the example is representative and how it was selected.
Circularity Check
Self-doubt reduction is measured by a rubric whose definition the prompt explicitly enforces, so the central mechanistic claim is partly circular; the engineering result remains self-contained.
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self definitional
[Section 2 (SD definition) and Section 3 / Table 2 (prompt)]
""Overthinking with Self-Doubt (SD): The model's answer includes unnecessarily long reasoning and repeatedly verifies information that is already correct." ... "otherwise, answer it with the minimum number of tokens required.""
The construct 'self-doubt' is defined by the presence of 'unnecessarily long reasoning' plus repeated verification of already-correct content. The intervention prompt explicitly instructs the model to 'answer it with the minimum number of tokens required,' which directly removes the first defining condition. Therefore the reductions in response length and judge-labeled self-doubt reported in Tables 1, 3, and 4 are entailed by the prompt instruction itself; they cannot serve as independent evidence that the mechanism 'reduced self-doubt' is what drives the improvement. The causal attribution 'alleviate overthinking by avoiding self-doubt' restates the instruction rather than testing an independent mechanism.
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self definitional
[Section 6, Table 4 paragraph]
""As shown in Table 4, our method reduces the self-doubt ratio in two out of three datasets, with a particularly notable 23.8% reduction on the complex dataset MATH-500, demonstrating our method can effectively reduce self-doubt.""
This 'self-doubt ratio' is computed with the LLM judge whose rubric is the Section 2 definition of self-doubt. Because the treated prompt explicitly demands the minimum number of tokens, the judge's criterion 'unnecessarily long reasoning' will almost mechanically flag fewer treated responses as self-doubt. The reported reduction therefore reflects the prompt's length constraint, not an independently measured change in a distinct psychological or mechanistic state. The paper's own Limitations section concedes the judge 'may misunderstand nuanced reasoning patterns or miss subtle verification steps,' and no human-validated alternative is provided, so the claim that self-doubt was the operative cause is not secured.
full rationale
The practical engineering result—that a prompt containing an explicit 'minimum number of tokens required' instruction reduces output length while often preserving or improving accuracy and abstention rates on the tested benchmarks—is self-contained and credible. The paper also correctly separates well-defined from missing-premise tasks and reports consistent gains. However, the central mechanistic claim (self-doubt significantly contributes to overthinking, and the proposed method works by reducing self-doubt) is partially circular: self-doubt is operationalized with a judge rubric that defines it as unnecessarily long reasoning with repeated verification, and the intervention directly instructs the model to use the minimum number of tokens. The measured reduction in self-doubt is thus aligned with the prompt by construction. No load-bearing self-citation or imported uniqueness theorem is present; the descriptive proportions in Figure 1 are not themselves circular, though the causal language around them is under-supported. Overall, the paper contains a significant definitional reduction in its key interpretative step, but the independent benchmark results prevent a higher score.
Assumptions & free parameters
assumptions (3)
- domain assumption The LLM judge Qwen2.5-72B-Instruct reliably classifies reasoning paths into self-doubt, overthinking-without-self-doubt, and non-overthinking categories.
- domain assumption Splitting responses at the paragraph delimiter and scoring only the second segment isolates self-doubt.
- ad hoc to paper Social comparison theory applies to LLM behavior and explains self-doubt as excessive deference to the user.
Cite this review
Pith. "Pith review of Revisiting Overthinking in Long Chain-of-Thought from the Perspective of Self-Doubt." pith.science (2026). https://pith.science/paper/QBAYXLYY
@misc{pith2026250523480,
author = {Pith},
title = {Pith review of: Revisiting Overthinking in Long Chain-of-Thought from the Perspective of Self-Doubt},
year = {2026},
howpublished = {\url{https://pith.science/paper/QBAYXLYY}},
note = {Machine review of arXiv:2505.23480}
}
read the original abstract
Reasoning Large Language Models (RLLMs) have demonstrated impressive performance on complex tasks, largely due to the adoption of Long Chain-of-Thought (Long CoT) reasoning. However, they often exhibit overthinking -- performing unnecessary reasoning steps even after arriving at the correct answer. Prior work has largely focused on qualitative analyses of overthinking through sample-based observations of long CoTs. In contrast, we present a quantitative analysis of overthinking from the perspective of self-doubt, characterized by excessive token usage devoted to re-verifying already-correct answer. We find that self-doubt significantly contributes to overthinking. In response, we introduce a simple and effective prompting method to reduce the model's over-reliance on input questions, thereby avoiding self-doubt. Specifically, we first prompt the model to question the validity of the input question, and then respond concisely based on the outcome of that evaluation. Experiments on three mathematical reasoning tasks and four datasets with missing premises demonstrate that our method substantially reduces answer length and yields significant improvements across nearly all datasets upon 4 widely-used RLLMs. Further analysis demonstrates that our method effectively minimizes the number of reasoning steps and reduces self-doubt.
Figures
Forward citations
Cited by 4 Pith papers
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Diagnosing and Mitigating Thinking Collapse in On-Policy Self-Distillation
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A Temporal Reasoning Benchmarking Framework for LRMs via Difficulty-controlled and Dynamic Test Generation
TRACEBench shows LRM temporal accuracy falls almost linearly with a controllable Allen-algebra difficulty score, while ~28% of mid-sized model successes are spurious guesses.
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BLADE: Boundary-Expanded and Layer-Adaptive Dynamic Exit for Efficient LLM Reasoning
BLADE stops LLM reasoning early at sentence and self-doubt boundaries using a layer-adaptive probe, cutting tokens ~25% with near-matched accuracy on five math benchmarks.
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Better Starts, Better Ends: Bootstrapped Iterative Self-Reasoning Distillation for Compressed Reasoning
Warm-starting on-policy self-distillation with a correctness-filtered, prompt-switched SFT bootstrap improves compression and accuracy of reasoning traces across math benchmarks.
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Reviewed August 7, 2026 · model on record in the stance chip above.
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