Anthropic
Microsoft fixes Claude Cowork on Windows, but doesn't say so
Anthropic said Sept. 14, 2026, that a Microsoft Windows update fixed the outage that had blocked Claude Cowork from running local commands.
Claude Cowork can run local commands on Windows again, and the fix came from Microsoft, not from a change on Anthropic’s side.
The trouble started with a Windows update released Sept. 8, 2026, according to Anthropic’s status page. In an update timestamped 15:54 UTC on Sept. 10, Anthropic said that update left Cowork on Windows unable to run local commands, because its workspace could no longer reach the user’s computer drive.
For most users, chat and file reading and editing still worked, the company said in that same update. There was no in-app workaround, and restarting or reinstalling the app would not help. Microsoft had developed a fix and was working to release it, Anthropic said.
That release came Sept. 14. In an update timestamped 19:14 UTC, Anthropic said the issue was resolved because Microsoft released a Windows update that day that fixes it, and linked to Microsoft’s support article for the update, KB5129195.
Microsoft’s own release notes for the update, dated Sept. 14, 2026, describe KB5129195 as an out-of-band cumulative update for Windows 11 versions 24H2 and 25H2, covering OS builds 26200.9457 and 26100.9457. The notes list four fixes: a security protection for CVE-2026-62721, an elevation-of-privilege vulnerability in the Windows User-Mode Power Service; a fix for Remote Desktop Services becoming unstable after the September 2026 security update KB5122880; a fix for Hyper-V-managed virtual machines that could not show or access folders shared from the Windows host using Plan9; and a fix for some USB Audio Class 1.0 devices failing on multichannel or 8-channel/3D audio modes.
Microsoft’s release notes do not mention Claude or Cowork anywhere in the update’s listed fixes.
Claude Cowork is one of Anthropic’s paid Claude plan features, alongside Claude Code, Claude Design and Claude Science, according to Anthropic’s pricing page.
Analysis
Anthropic named the update that fixed its product. Microsoft’s own account of that update does not name Anthropic’s product at all. Neither company has said which of the four listed fixes, if any, was the one that mattered. For six days, a company whose software depends on another company’s infrastructure was waiting on a fix it could not describe and could not ship itself.