[BUG] - Intermittent ECONNRESET / "undefined Connection error" in VS Code extension

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?

Frequent intermittent connection failures during normal Claude Code usage in VS Code. The extension retries up to 11 attempts before failing. Errors occur mid-session — some requests succeed, others fail repeatedly.

What Should Happen?

Stable API connectivity throughout the session.

Error Messages/Logs

2026-02-27T19:30:39.024Z [ERROR] API error (attempt 5/11): undefined Connection error.
2026-02-27T19:30:48.421Z [DEBUG] Fast mode unavailable: Fast mode requires extra usage billing · /extra-usage to enable
2026-02-27T19:30:56.339Z [ERROR] API error (attempt 6/11): undefined Connection error.
2026-02-27T19:31:13.690Z [DEBUG] Fast mode unavailable: Fast mode requires extra usage billing · /extra-usage to enable
2026-02-27T19:31:18.620Z [ERROR] API error (attempt 7/11): undefined Connection error.



User-facing error: API Error: Unable to connect to API (ECONNRESET)

Steps to Reproduce

1. Use Claude Code normally in VS Code
2. Some requests succeed, others fail with ECONNRESET
3. Retries exhaust without recovering

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.61

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

VS Code integrated terminal

Additional Information

Troubleshooting performed
All local network diagnostics pass:

1. DNS: Resolves api.anthropic.com correctly (160.79.104.10)
2. TLS: Succeeds with TLSv1.3 / TLS_AES_256_GCM_SHA384
3. Latency: ~2.8ms, 0% packet loss
4. curl: Full round-trip in 261ms
5. Firewall: No blocks
6. The connection works intermittently in the same session, suggesting a server-side issue.

Fast mode unavailable debug messages appear interleaved with connection errors — unclear if related.
status.claude.com showed resolved incidents on 2026-02-27, but errors persisted after resolution was posted.