{"type":"post","id":"lessons-from-building-copilot-cowork-21-minute-read-01943f","slug":"lessons-from-building-copilot-cowork-21-minute-read-01943f","title":"Lessons from building Copilot Cowork","description":"Microsoft says nine engineers built Copilot Cowork from an empty repository to worldwide general availability in about four and a half months, with agents writing most of the code.","retrieval_nugget":"Microsoft says nine engineers built Copilot Cowork from an empty repository to worldwide general availability in about four and a half months, with agents writing most of the code. Its account details a spec-first workflow, parallel narrow agents, automated review and a trusted execution boundary—practical lessons for teams scaling agent-assisted software development.","published_at":"2026-11-03","updated_at":"2026-11-06","record_date":"2026-11-03","date_kind":"published_at","topics":["agent-security"],"entities":["Microsoft","Copilot Cowork","Work IQ","Bas Brekelmans"],"related_patterns":["agent-security-moves-to-runtime-boundaries","verification-bandwidth-is-the-scarce-resource"],"novelty_label":"new_fact","what_changed":"Adds Microsoft’s engineering account of building Copilot Cowork, including its Python-to-Rust live migration, four-and-a-half-month path to worldwide GA, and 1,211 pull requests merged by nine engineers in a day.","prior_refs":["https://newruntime.com/posts/daily-ai-brief-sept-26-microsoft-biggest-copilot-a0fd1e/"],"source_url":"https://commandline.microsoft.com/how-we-built-copilot-cowork-python-to-rust-migration","source_urls":["https://commandline.microsoft.com/how-we-built-copilot-cowork-python-to-rust-migration"],"schema_version":"newruntime-agent-readable-v0.2","stable_id":"post:lessons-from-building-copilot-cowork-21-minute-read-01943f","status":"published","visuals":[],"editor":{"role":"editor","name":"Andrey Reshetnikov","profile":"https://newruntime.com/owner-profile.md","profile_json":"https://newruntime.com/owner-profile.json","same_as":["https://www.linkedin.com/in/reshetnikov1/","https://t.me/lapetuse"]},"routes":{"html":"https://newruntime.com/posts/lessons-from-building-copilot-cowork-21-minute-read-01943f/","markdown":"https://newruntime.com/posts/lessons-from-building-copilot-cowork-21-minute-read-01943f.md","json":"https://newruntime.com/posts/lessons-from-building-copilot-cowork-21-minute-read-01943f.json"},"markdown_url":"https://newruntime.com/posts/lessons-from-building-copilot-cowork-21-minute-read-01943f.md","next_reads":[{"type":"topic","path":"/topics/agent-security/","url":"https://newruntime.com/topics/agent-security/","title":"Agent Security","reason":"Explore the agent-security topic hub.","media_type":"text/html","markdown_url":"https://newruntime.com/topics/agent-security.md","json_url":"https://newruntime.com/topics/agent-security.json"},{"type":"collection","path":"/posts/","url":"https://newruntime.com/posts/","title":"Field Notes","reason":"Open the latest editorial analysis.","media_type":"text/html","json_url":"https://newruntime.com/posts.json"},{"type":"collection","path":"/sources/","url":"https://newruntime.com/sources/","title":"Sources","reason":"See the original sources this archive cites.","media_type":"text/html"}]}