METR's RCT: AI tools made experienced maintainers 19% slower | CodexMaster

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July 10, 2025milestonechronicleThe Agent Era

METR's RCT: AI tools made experienced maintainers 19% slower

In a randomized trial on mature open-source repos, developers using early-2025 AI tools took 19% longer — while believing they were 20% faster. The single most-cited caution of the era: measure your own workflow, because perception is not throughput.

Sources

metr.org
arxiv.org

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