A 2025 study from METR found that experienced developers using AI coding tools like Cursor and Claude were 19% slower on real-world tasks. Despite their expertise, these developers incorrectly predicted a 24% speed boost. The research reveals a paradox where seasoned coders, working on complex legacy codebases, faced high rejection rates and context-switching overhead with AI suggestions.

This slowdown contrasts sharply with studies on junior developers, who saw productivity gains of 21-40%. The key difference isn't raw coding skill but metacognition: knowing when to trust AI, what to ask for, and when to code manually. Senior developers using AI for production deployments 2.5x more often demonstrate this contextual awareness.

The findings suggest traditional coding assessments are outdated. In an era where 41% of code is AI-generated, effective 'vibe coding' requires skills like prompt engineering, communication, and system design thinking. The real measure of a developer may soon be their ability to guide AI, not just to write algorithms.