Cohere Labs and others publish The Leaderboard Illusion
Published The Leaderboard Illusion — Google receives 19.2% and OpenAI 20.4% of Arena data, while 83 open-weight models combined receive 29.7%. Providers can test multiple private variants and then retract scores
Why it matters
Demonstrated the structure of leaderboard overfitting. The reason Arena rankings should not be read as a direct measure of capability
Source — Primary sources first; secondary reports are labelled “Press”
Paperarxiv.orghttps://arxiv.org/abs/2504.20879Added in Week 35, 2026 · See that week