We conduct a randomized controlled trial (RCT) to understand how early-2025 AI tools affect the productivity of experienced open-source developers working on their own repositories. Surprisingly, we find that when developers use AI tools, they take 19% longer than without—AI makes them slower.
So, speed isn’t everything, and the biggest problem with A.I. coding is long-term quality. However, most participants *thought* they were faster with Cursor when they actually weren’t. To me, this is the most interesting finding: the power of the hype.