[BUG] Cowork sandbox fails to start on macOS after June 10 app update: "Workspace unavailable... Download failed"

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Since the Claude desktop app auto-updated on June 10, 2026 (~12:14 GMT+3), the Cowork isolated Linux workspace (sandbox) cannot start on macOS. Every bash call in every Cowork session fails.

Timeline of errors:

• First hours: "Workspace still starting. The isolated Linux environment is booting in the background" — forever, it never finishes.
• Then: "Workspace unavailable. The isolated Linux environment failed to start (Request error: net::ERR_CONNECTION_CLOSED)".
• After full app reinstall: "Workspace unavailable. The isolated Linux environment failed to start (Download failed. Check your internet connection and try again.)" — the sandbox image download never succeeds.

Everything else works: chat, file tools, web_fetch, Claude in Chrome extension, Claude Code mode. Internet connection is fine. The June 10 Cowork incident on status.claude.com was resolved, but this machine still cannot download/start the sandbox days later.

Impact: all bash-dependent functionality in Cowork is unusable (scheduled tasks, data analysis pipelines).

Note: similar reports from Windows users exist (e.g. #55649, #56145, #57968) — this report documents the same class of failure on macOS, clearly triggered by the June 10 app update.

What Should Happen?

The Cowork isolated Linux workspace (sandbox) should boot normally so bash commands can run, as it did before June 10.

Error Messages/Logs

Workspace still starting. The isolated Linux environment is booting in the background (usually 10-30 seconds). Try again shortly.

Workspace unavailable. The isolated Linux environment failed to start (Request error: net::ERR_CONNECTION_CLOSED). You can still use file tools directly.

Workspace unavailable. The isolated Linux environment failed to start (Download failed. Check your internet connection and try again.). You can still use file tools directly.

Steps to Reproduce

1. Claude desktop app auto-updated on June 10, 2026 at ~12:14 GMT+3 (Cowork sandbox worked fine before that moment).
2. Open any Cowork session (new or existing) and ask Claude to run any bash command, e.g. echo ok.
3. For the first hours every call returned "Workspace still starting...", then "failed to start (Request error: net::ERR_CONNECTION_CLOSED)".
4. After a full reinstall of the app the error changed to "failed to start (Download failed. Check your internet connection and try again.)" - the sandbox image download never succeeds.

Tried without success: app restart, Mac reboot, macOS update, full app reinstall, VPN in different modes (direct/global/off). Chat, web_fetch, Claude in Chrome and Claude Code mode all work fine - only the Cowork sandbox is broken. Reproduces in all new chats/sessions since June 10. Support ticket (Intercom) ID: 215474649684162.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude desktop app (Cowork), fresh install from claude.ai on June 11, 2026 - latest available. Cannot run claude --version inside Cowork because the sandbox does not start; the report is about the desktop app sandbox, not the CLI.

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Environment: MacBook (Apple Silicon), 24 GB RAM, 700+ GB free disk, macOS 26.5 (25F71). Claude desktop app reinstalled fresh on June 11 - same problem. Region: Russia, Claude is used via VPN; tested several VPN exit locations, VPN global mode and VPN fully off - the sandbox image download fails in every configuration while all other Claude endpoints are reachable. Support ticket (Intercom) ID 215474649684162 with the same details was escalated to a human agent on June 11.