CoPilot has suddenly stopped working in Word?

Since the failure happens in Word desktop and web on two Windows versions, while Copilot works in other Microsoft 365 apps, it does not look like one damaged Word installation. It is more likely a Word-specific service, document, account, or tenant condition, so record the time and test with a new blank document stored in OneDrive. That distinguishes a document-specific problem from the Word service path. Verify the affected account is the licensed account in Word, sign out and back in once, and install the latest Office updates. Check the Microsoft 365 admin center’s service health for Word or Copilot advisories. If the blank document fails in both clients and service health is clear, collect the Word version, browser version, tenant, approximate timestamps, and any request ID shown with the error, then reopen the Microsoft support case. No client-side repair can prove a server-side Word Copilot fault is resolved.