METR is a research nonprofit that studies AI systems, and this February 2026 post is a rare thing: an institute reporting that its own measurement stopped working, before anyone forced the issue.

The setup is short. METR's earlier trial, run on data from February to June 2025, found that experienced open-source developers were about 20% slower when they used AI tools. To track how that changes over time, METR started a second experiment in August 2025 with a larger pool of developers and the latest tools. The update is that this new data gives an unreliable signal of the current productivity effect.

Three reasons are named, and all of them push the estimate the same way. Developers increasingly chose not to take part because they did not want to work without AI. The pay rate was cut from $150 an hour to $50, which changes who signs up. And time-on-task measurement is unreliable for the developers running several AI agents concurrently. METR's own read is that developers are likely more sped up in early 2026 than the 2025 figure implies, but that their data is only very weak evidence for the size of that increase, so the task-level design has to change.

The trade-off is that you get no new number here. If you came for a fresh productivity estimate, this will frustrate you. What you get is an honest account of how an experiment gets overtaken by the thing it measures.