AI made experienced devs 19% slower. Here's the side project trap that created.
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METR measured it in 2025 — senior devs with AI coding assistants worked 19% slower and thought they were 43% faster. For side projects, this gap is career-ending for your product. In July 2025, METR ran a controlled trial with experienced software developers using AI coding assistants. The result: they worked 19% slower than without AI tools. Not faster. Worse: they thought they were working 43% faster. A 62-percentage-point gap between perception and reality. I kept thinking a