Microsoft has launched Copilot Cowork, its most ambitious M365 AI feature yet, and it runs on Anthropic's Claude engine. The feature is a cloud-based AI agent that executes multi-step tasks across Microsoft 365 applications autonomously — drafting documents in Word, building spreadsheets in Excel, scheduling in Outlook, and coordinating through Teams, all from a single natural language instruction.
The decision to build Cowork on Claude rather than OpenAI's models is a significant strategic signal. Microsoft has been OpenAI's primary investor and partner, but the choice to use Claude for its flagship agentic feature suggests that Anthropic's models outperformed in the specific capability profile that Cowork requires — sustained multi-step reasoning, reliable instruction following, and safe autonomous execution.
Separately, Claude Sonnet is now selectable as an alternative model in Copilot Chat for all licensed M365 users outside EU/EFTA, UK, government, and sovereign clouds. The rollout completes by late March 2026. For developers and teams already familiar with Claude's behaviour from coding tools, having the same model available in their productivity suite creates a consistent AI experience across their workflow.
