AI Makes Experienced Developers Slower. Here's Why.

AI Makes Experienced Developers Slower. Here's Why. By Vítor Andrade Earlier this year, METR published a randomised controlled trial that should have shaken every engineering organisation awake. They took experienced open-source developers, gave them state-of-the-art AI coding tools, and measured what happened. The developers got 19% slower. Not junior developers. Not people unfamiliar with the codebases. Experienced contributors working on projects they knew intimately, with tools they chose themselves. And here is the part that should genuinely unsettle you: those same developers believed they were 24% faster. A 43-percentage-point gap between perception and reality. The engineers most qualified to judge were the most wrong. I have spent the past year helping engineering teams integrate AI agents into their workflows. I have watched this pattern play out dozens of times. A senior developer picks up Cursor or Claude Code, feels the rush of generating code at unprecedented speed, and s