# Microsoft — Nine engineers, 1,211 pull requests in a day: Lessons from building Copilot Cowork

- Company: Microsoft (microsoft.com)
- Announced: 2026-11-02T15:13:56+00:00
- Category: not stated
- Coverage: not counted
- Announcement: no
- Group: routine
- Source: https://commandline.microsoft.com/how-we-built-copilot-cowork-python-to-rust-migration/
- Record: https://forck.live/items/30555-nine-engineers-1-211-pull-requests-in-a-day-lessons-from-building-copilot-cowork
- Subject: Foundry / Responsible AI

In January of this year, a small team at Microsoft set out to build Copilot Cowork , an agentic execution layer that performs multi-step workflows on a user’s behalf. That result brings the powerful AI-assisted tools and capabilities developers have today to everyday knowledge workers, all with Work IQ , Microsoft 365 security and governance, cloud execution, and Microsoft’s multi-model architecture. This is the story of how the team took Copilot Cowork from an empty repo to worldwide GA in about four and a half months, then moved its runtime from Python to Rust while it was live. Agents wrote most of the code. Ways of working changed along the way, and the practices other teams can adapt to build like a frontier development team: moving fast while keeping reliability, security, and cost in view. On October 21, nine engineers merged 1,211 pull requests into the main branch of the Copilot Cowork backend. That number would have sounded absurd to the team in January, when a handful of us made the first commit to an empty repo. Agents wrote most of the code, but engineers remained responsible for defining the work and judging the results. …

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Record: https://forck.live/items/30555-nine-engineers-1-211-pull-requests-in-a-day-lessons-from-building-copilot-cowork
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