**[BUG] Cowork: `coworkd_upstream_failed` / `tls: bad record MAC` — cannot start Cowork session**

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?

Every attempt to start a new Cowork session fails immediately with the following error:

API Error: 587 {"error":"coworkd_upstream_failed","category":"unknown","detail":"remote error: tls: bad record MAC"}

The error has been occurring all day. Restarting Claude Desktop does not resolve it. Regular chat mode works fine — only Cowork is affected.

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Steps to reproduce

1. Open Claude Desktop (v1.1.9493) on macOS
2. Navigate to Cowork
3. Attempt to start a new Cowork session
4. Error appears immediately

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Notes

The bad record MAC error suggests a TLS handshake or packet integrity failure between the Cowork VM and Anthropic's upstream servers — likely a server-side infrastructure issue rather than a client misconfiguration. This coincides with the elevated Cowork connection reset errors reported on status.claude.com over the past several days.

What Should Happen?

Cowork session starts successfully.

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Actual behavior

Session fails with coworkd_upstream_failed and a TLS bad record MAC error (error code 587).

What I've tried

• Restarted Claude Desktop — issue persists
• Already on latest version (1.1.9493)
• Regular chat works fine, so this appears isolated to the Cowork VM/upstream connection

Error Messages/Logs

API Error: 587 {"error":"coworkd_upstream_failed","category":"unknown","detail":"remote error: tls: bad record MAC"}

Steps to Reproduce

1. Open Claude Desktop (v1.1.9493) on macOS
2. Navigate to Cowork
3. Attempt to start a new Cowork session
4. Error appears immediately

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

v1.1.9493

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_