The Compound Developer

In the most rigorous study of AI coding tools conducted to date — a randomized controlled trial by METR published in July 2025 — sixteen experienced open-source developers used AI assistance on tasks in their own projects. Projects they had worked on for an average of five years. Before each task, they predicted AI would reduce their completion time by 24%. After each task, they estimated they had been sped up by 20%.
The actual measurement: they were 19% slower.

The perception-reality gap in that study is between 39 and 44 percentage points. The developers were not exaggerating. Working with AI genuinely feels faster. But something in the translation from felt experience to measured outcome goes wrong — and understanding what, exactly, goes wrong is the only path to what actually works.

