AI Systems Atlas

E-14Task Sets & Contamination

/evals/task-sets-and-contamination

Where benchmark tasks come from, and what happens to a benchmark once it is published.

Step-by-step walkthrough6 steps
  1. Tasks come from where the agent actually fails, not from what is convenient to write.
  2. Synthetic cases fill coverage gaps — they are the seasoning, never the meal.
  3. Curation is the work: too easy and every change looks neutral, too hard and every change looks the same.
  4. Part of the set can be published, so results are comparable.
  5. And a published set gets scraped. Next year’s model has read your answers.
  6. A held-out set never leaves the building — the gap between the two scores tells you how contaminated the public one is.
Key insight

Draw tasks from where the agent actually fails, and keep a held-out set that never ships. The gap between your public score and your private one is a direct measurement of how contaminated the public one has become.

Failure mode

Trusting a public benchmark years after publication. Once it is in the training data, you are measuring recall of the answer key, not capability.

Further reading
RelatedRegression evalsOffline vs onlineAdversarial evalsBenchmark saturation

Elsewhere in the atlas

Harnesses →Security →Context →Coding Agents →Tools →Ops →