Measuring the Impact of Early-2025 AI on Experienced Open-Source Developer Productivity: https://metr.org/blog/2025-07-10-early-2025-ai-experienced-os-dev-study/
METR ran a controlled experiment with 16 experienced open-source developers on 246 programming tasks. The developers predicted that the use of AI would speed up their work by 25%, and after the experiment judged that it had sped it up by 20%. But when actually measured, the use of AI slowed down their work by 19%.