REVIEW 5 major objections 4 minor 34 references
LLM Performance for Code Generation on Noisy Tasks
T0 review · 5 major / 4 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read This paper claims that LLMs solve heavily obfuscated coding and math tasks through memorisation and eager pattern matching, not genuine reasoning, and that the rate of performance decay under obfuscation can serve as a practical detector…
desk verdict A real, reproducible asymmetry in how LLMs handle obfuscated old vs. new LeetCode tasks; the decay-as-contamination detector is plausible but unproven because the comparison isn't difficulty-matched. 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 machinery is an obfuscation pipeline that applies three augmentation methods (typos, random word deletions, and truncation) at ten severity levels to twenty tasks per dataset, creating 600 obfuscated variants that are scored by automated test cases. The load-bearing quantity is the performance-decay curve, summarised by the 50%-decay augmentation rate, which the paper uses to separate contaminated from uncontaminated content. The named behaviour 'eager pattern matching' is the paper's explanation for why models succeed where humans cannot: instead of reconstructing the question, the model pattern-completes toward a memorised exemplar, a mechanism tested with adversarial tasks that resemble familiar problems but ask a different question.
What would settle it
Fine-tune a model on a set of post-cutoff tasks, re-run the obfuscation sweep, and check whether the decay curve flattens to the OldLC shape; if it stays steep, gentler decay is not caused by memorisation and the proposed contamination detector fails.
Extended reading notes
Core claim
The paper's central claim is that all five evaluated LLMs solve tasks obfuscated beyond human recognition when those tasks predate the models' training data, and that this success is an artefact of memorisation, not reasoning. On LeetCode tasks published in 2015, models continued to produce correct solutions even at maximum obfuscation, while not one model solved any of the 2025 task versions obfuscated above a 0.7 augmentation rate. The authors introduce 'eager pattern matching' to describe the mechanism: the model seizes on residual stylistic cues and answers with a complete solution to a similar training problem, which they demonstrate with adversarial variants of known tasks that all models solved incorrectly by reproducing the memorised answer. They report that the augmentation rate causing 50% performance loss is roughly twice as high on the old dataset as on the new one, and treat this decay contrast as evidence that the old tasks are in the training set.
Load-bearing premise
The comparison that carries the contamination conclusion assumes old and new LeetCode tasks are interchangeable except for publication date, but the new tasks already score far lower without obfuscation, so their faster decay could come from being harder rather than from being unseen during training.
Editorial extensions
If this is right
- Benchmark scores on static, widely copied datasets can materially overstate how well an LLM can reason about unfamiliar problems.
- A model that eagerly matches patterns may produce confident, wrong solutions when a new task superficially resembles a training problem, creating a safety hazard for automated code generation.
- Measuring the obfuscation-decay curve offers a low-cost, model-agnostic check for whether a dataset is likely to be in a model's training data.
- Evaluations on newly released tasks, and dynamic benchmarks that avoid reuse, become necessary for trustworthy capability claims.
Reading between the lines
- The paper does not run the decisive control of deliberately training a model on a post-cutoff task and re-measuring its decay curve; if the curve then flattened, the memorisation mechanism would be confirmed, and if not, the decay contrast would be explained by task difficulty rather than contamination.
- A practical contamination detector would need to separate decay due to memorisation from decay due to question length or style; fitting per-model decay curves on more datasets, as the paper itself suggests, is a testable next step.
- The eager-pattern-matching result implies that human review of AI-generated code may be insufficient when the input prompt resembles a training example, because the model will confidently reproduce the wrong solution; a natural extension is testing such adversarial prompts in an IDE-style assistant.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies how LLMs behave on obfuscated competitive-programming and math tasks. It compares five LLMs on three datasets: OldLC (LeetCode questions from 2015), NewLC (LeetCode questions from March 2025, after the models' knowledge cutoffs), and MATH (2021). Using three obfuscation methods (Typos, Deletions, Truncation) at ten augmentation levels, the authors measure accuracy decay and find that OldLC and MATH tasks are solved even under extreme obfuscation while NewLC tasks are not, concluding that LLMs rely on memorisation and 'eager pattern matching' rather than reasoning. The paper proposes performance-decay statistics (e.g., 50% decay point) as a potential contamination detector, supports this with adversarial examples that show LLMs reverting to known problems, and discusses safety and evaluation implications. The repository with code and data is provided.
Significance. If the central empirical contrast is trustworthy, the paper makes a useful contribution: it provides a concrete, reproducible procedure (obfuscation + decay analysis) for probing contamination, releases code and data, and includes adversarial tasks that go beyond simple memorisation checks. The observation that LLMs solve tasks that humans judge unintelligible is striking and worth reporting. However, the paper's own conclusions are more cautious than its abstract: Section VI concedes that confounding factors cannot be ruled out with three summary statistics. The significance therefore hinges on whether the OldLC/NewLC comparison can be made difficulty-matched, and whether the correctness metric is strong enough to support the claims.
major comments (5)
- [IV.A, Table II, Table I] The central contamination signal is the contrast between slow decay on OldLC (50% decay at 0.70 ± 0.08) and fast decay on NewLC (50% decay at 0.29 ± 0.06). This comparison is confounded by baseline difficulty: Table II shows that non-obfuscated accuracy on NewLC (0.19–0.45 across models) is far below OldLC (0.50–0.66). With a lower baseline, the same absolute accuracy drop occurs at a lower augmentation level simply because of floor effects; the 50% decay point is not difficulty-invariant. The paper states in IV.A that the two LeetCode sets are 'very similar tasks,' but that claim is not supported by the baseline gap. To make the decay-as-contamination claim load-bearing, the authors should either match tasks by difficulty, normalize decay relative to baseline accuracy, or show that the OldLC/NewLC difference persists on a difficulty-matched subset. The MATH results (high baseline, yet steep initial decay, 50% decay at 0.19) further show that baseline alone does not determine decay, but they also show that decay behavior is dataset-specific, so without controlling for difficulty the OldLC/NewLC contrast cannot isolate contamination.
- [III.D, IV.A] Correctness for coding tasks is judged on the 2–3 test cases embedded in the problem statement. This is a very weak proxy for a correct solution: a memorised solution that happens to pass the provided examples may be counted correct even if it does not solve the general problem. Given that the paper's headline claim is that LLMs 'solve' obfuscated tasks, the metric should be strengthened (e.g., a held-out test set from LeetCode's official test suite, or at least a larger set of generated test cases). The current metric allows the decay curves to be contaminated by false positives, and the contrast between OldLC and NewLC could be partly an artefact of OldLC tasks having more memorable input-output pairs.
- [IV.B, Table I] The interpretation of the MATH results is internally strained. The paper notes that MATH shows a steep initial decay (50% decay at 0.19), which 'could suggest a lower degree of overtraining or perhaps not being included in the training set at all,' but then rejects this possibility because tasks are still solved at high obfuscation, attributing the difference to question length and redundancy. This is an ad hoc explanation: if length/redundancy explains the MATH pattern, then it may also explain part of the OldLC/NewLC difference, since LeetCode and MATH are not matched on length, redundancy, or style. The decay detector therefore lacks a well-defined null model. The authors should either provide a quantitative model of how redundancy interacts with decay, or explicitly restrict the contamination-detection claim to comparisons within a matched dataset family.
- [III.F, Fig. 8] The human baseline measures self-reported understanding of obfuscated text, not actual problem-solving ability. The paper acknowledges this ('It is not directly comparable to actual performance'), but Figure 8 presents the human baseline as a decay curve alongside LLM decay, and the text uses it to argue that LLMs exceed 'human recognition' thresholds. Since the baseline is subjective and based on randomly selected examples rather than the full task set, it cannot support quantitative claims such as 'obfuscated beyond human recognition.' Either collect a more rigorous human performance baseline (e.g., asking participants to solve the tasks) or soften the wording to 'self-reported comprehensibility.'
- [VI, IV.A, V] The proposed contamination detector is essentially the same observation used to infer contamination: slow decay on assumed-contaminated OldLC versus fast decay on assumed-clean NewLC. There is no out-of-sample validation. The paper explicitly concedes (Section VI) that with only three sets of summary statistics, confounding factors cannot be ruled out. This is an honest limitation, but it should be reflected in the abstract and in the contributions list, which state that decay 'is a practical indicator of dataset contamination' and 'reveals stark differences between new and contaminated tasks.' As it stands, the paper demonstrates a correlation between release date and decay behavior on one pair of datasets; the detection claim is a hypothesis, not a validated method. The authors should either add a validation experiment (e.g., training a model on a known subset of an older dataset and testing on held-out versions) or explicitly reframe the contribution as a proposed diagnostic with preliminary evidence.
minor comments (4)
- [Throughout] Several typos and grammatical slips should be corrected: 'augmention' (IV.A), 'previosly' (Appendix D), 'contaminaton' (II.A), 'which is not surprising as it's currently top' (Appendix C.A).
- [Fig. 4] The adversarial example in Figure 4 has 'nums[2]' in the constraints, which appears to be a typo for 'nums2[i]'; this is potentially confusing for a reader trying to verify what the LLM was asked.
- [III.F] The description of the human baseline says '4 researchers with a high level of coding and math skills' but does not specify how many examples each participant saw, how the random selection was performed, or whether participants were aware of the original task content; please provide more detail for reproducibility.
- [References] Reference [33] appears to be miscited: the listed DOI (10.1145/3643657.3643910) belongs to the S4 workshop paper, not the Hawaii conference paper; please verify and correct.
Circularity Check
No significant circularity: the core obfuscation experiments are self-contained; the contamination-detector proposal is a conceded hypothesis rather than a fitted prediction.
full rationale
The paper's main empirical contributions are self-contained. The obfuscation pipeline, the collection of OldLC, NewLC, and MATH tasks, the model API evaluations, and the adversarial 'two medians' task are all external observations: no equation defines the target claim in terms of its own evidence, and no fitted parameter is renamed as a prediction. The OldLC-versus-NewLC decay contrast is a measured empirical difference, and the assumption that OldLC is contaminated rests on release-date reasoning independent of the decay measurement. The proposed decay-based contamination detector is presented as a hypothesis, not as a validated tool; Section VI explicitly concedes: 'with just three sets of summary statistics, we are unable to account for confounding factors or test any such detection systems.' That concession is a limitation and a validity gap, but it is not a definitional reduction. The paper also contains author self-citations ([32], [33]) supporting the intellectual-debt discussion, but these are not load-bearing for the experimental claims. Overall, there is no circular step that equates an input to an output by construction, so the circularity score is low.
Assumptions & free parameters
assumptions (3)
- domain assumption OldLC tasks are included in the training data of all five LLMs, while NewLC tasks are not.
- domain assumption Passing all provided test cases (2-3 per problem) constitutes solving a coding task.
- domain assumption Human researchers' self-reported ability to understand obfuscated tasks is a valid baseline for 'unintelligible to human readers.'
invented entities (1)
-
eager pattern matching
Cite this review
Pith. "Pith review of LLM Performance for Code Generation on Noisy Tasks." pith.science (2026). https://pith.science/paper/HWOIUU35
@misc{pith2026250523598,
author = {Pith},
title = {Pith review of: LLM Performance for Code Generation on Noisy Tasks},
year = {2026},
howpublished = {\url{https://pith.science/paper/HWOIUU35}},
note = {Machine review of arXiv:2505.23598}
}
read the original abstract
This paper investigates the ability of large language models (LLMs) to recognise and solve tasks which have been obfuscated beyond recognition. Focusing on competitive programming and benchmark tasks (LeetCode and MATH), we compare performance across multiple models and obfuscation methods, such as noise and redaction. We demonstrate that all evaluated LLMs can solve tasks obfuscated to a level where the text would be unintelligible to human readers, and does not contain key pieces of instruction or context. We introduce the concept of eager pattern matching to describe this behaviour, which is not observed in tasks published after the models' knowledge cutoff date, indicating strong memorisation or overfitting to training data, rather than legitimate reasoning about the presented problem. We report empirical evidence of distinct performance decay patterns between contaminated and unseen datasets. We discuss the implications for benchmarking and evaluations of model behaviour, arguing for caution when designing experiments using standard datasets. We also propose measuring the decay of performance under obfuscation as a possible strategy for detecting dataset contamination and highlighting potential safety risks and interpretability issues for automated software systems.
Figures
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Reference graph
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Reviewed August 7, 2026 · model on record in the stance chip above.
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