An audit finds the most-cited preference leaderboard is optimised rather than merely measured
Singh and colleagues analysed roughly two million pairwise battles across 243 models from 42 providers over sixteen months of a public human-preference leaderboard. They reported undisclosed private testing under which a provider could evaluate many variants and publish only the best — one provider tested 27 private variants before releasing one publicly — that up to 26.5% of prompts were duplicates or near-duplicates, and that fine-tuning on arena-style prompts raised an arena win rate by 112% with no gain, or a slight loss, on general benchmarks. The last result is the important one: it separates performing well on the instrument from performing well on the thing the instrument was meant to stand for.
Observed — measured or witnessed, with the observation cited.
Subjects
- The difficulty of evaluating machine learning systems · phenomenon · not located
- Construct validity in AI evaluation · concept · not located
- Benchmark saturation · phenomenon · not located
Evidence
Verified — Every field is supported by a cited authoritative source.
The Leaderboard Illusion
A systematic study of roughly two million pairwise battles across 243 models from 42 providers over sixteen months (January 2024 – April 2025) of a leading public human-preference leaderboard found undisclosed private testing allowing providers to evaluate multiple variants and publish only the best — one provider tested 27 private variants before a public release — that up to 26.5% of prompts were duplicates or near-duplicates, that proprietary models received a disproportionate share of evaluation data, and that fine-tuning on arena-style prompts raised an arena win rate by 112% with no improvement, or a slight decline, on general benchmarks such as MMLU. V55 verification basis: the paper was not fetched, but search results carried the author list, the arXiv identifier 2504.20879, and each of these figures with attribution to this paper.
NeurIPS 2025; Cohere Labs and collaborating institutions · 2025-04 · Verified
Singh, S., Nan, Y., Wang, A., D'souza, D., Kapoor, S., Üstün, A., Koyejo, S., Deng, Y., Longpre, S., Smith, N., Ermis, B., Fadaee, M. and Hooker, S., arXiv:2504.20879; NeurIPS 2025
Recorded on The difficulty of evaluating machine learning systems
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- A human-parity claim in translation fails under document-level evaluation
- An audit finds the most-cited preference leaderboard is optimised rather than merely measured
- A systematic review of 445 benchmarks reports pervasive validity failures
- A randomised trial finds experienced developers slower with AI assistance
- The Commission proposes deferring the high-risk obligations
- The AI Index records both fast benchmark movement and doubts about benchmarks
Related
Related because they share a subject in the Atlas — never because the text looks similar.
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- GLUE is saturated and SuperGLUE is built to replace it · 2018–2019
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