[BUG] Severe latency on Sonnet 4.6 in VS Code extension despite green status page (Jun 6, 2026)

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?

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

Environment

• Extension version: anthropic.claude-code v2.1.167 (also tested with previous version after downgrade — same behavior)
• VS Code version: [preencher: Help → About]
• OS: Windows 11
• Plan: Claude Pro
• Model: Sonnet 4.6 (default)

What's Wrong?

The Claude Code VS Code extension is experiencing severe, intermittent latency on Sonnet 4.6. Requests that normally complete in seconds are taking minutes, and some fail entirely with ECONNRESET. This started on Jun 6, 2026 and has persisted for several hours.

The same project has been used daily for weeks with no performance issues. It's a small university project — not a large codebase, no heavy indexing expected.

Symptoms

• Requests intermittently fail with: API Error: Unable to connect to API (ECONNRESET)
• When requests succeed, response time is drastically higher than normal
• Image uploads on claude.ai (browser) also failed earlier today with: "O upload falhou devido a um problema de rede"
• Behavior occurs on Sonnet 4.6 (default model), not just Opus

Status Page Context

status.claude.com reported incidents on Opus 4.8 today (resolved at 19:05 UTC and 10:14 UTC), but my issues are on Sonnet 4.6 and persist after both incidents were marked resolved. No active incident covers what I'm experiencing.

Steps to Reproduce

1. Open VS Code with the Claude Code extension installed
2. Send any message in the chat panel using Sonnet 4.6
3. Observe extreme latency or ECONNRESET errors

What I've Tried

• Reloaded VS Code window (Developer: Reload Window)
• Downgraded extension to an earlier version — same behavior
• Switched models — Sonnet 4.6 also affected, not just Opus
• Tested network connectivity to api.anthropic.com directly via PowerShell:
• GET https://api.anthropic.com → 404 (expected, route resolves)
• POST https://api.anthropic.com/v1/messages with dummy key → 401 (expected, auth reached)
• Confirms network/firewall/antivirus are NOT the cause — the API is reachable normally
• Verified no VPN, no proxy, no third-party antivirus interfering

Expected Behavior

Requests on Sonnet 4.6 complete in normal time (seconds), as they did for weeks before today.

Additional Notes

This appears to be an undeclared performance degradation — the status page reports errors (5xx, failed requests), but not latency. "All green + severely slow" may indicate capacity or routing issues not currently being monitored.

What Should Happen?

Requests on Sonnet 4.6 should complete in normal response time (a few seconds for a small university project), as they consistently did for several weeks prior to Jun 6, 2026. The extension should not return ECONNRESET errors when the network connection to api.anthropic.com is verified to be working correctly.

Error Messages/Logs

API Error: Unable to connect to API (ECONNRESET)

Network diagnostics from PowerShell (confirming API is reachable):

> Invoke-WebRequest -Uri "https://api.anthropic.com"
Result: 404 (expected — route resolves correctly)

> Invoke-WebRequest -Uri "https://api.anthropic.com/v1/messages" -Method POST -Headers @{"x-api-key"="test"; "anthropic-version"="2023-06-01"; "content-type"="application/json"} -Body '{"model":"claude-opus-4-5","max_tokens":10,"messages":[{"role":"user","content":"hi"}]}'
Result: 401 Unauthorized (expected — auth endpoint reached normally)

These tests confirm the network path to Anthropic's API is healthy. The ECONNRESET occurs only through the Claude Code extension, not on direct API calls.

Steps to Reproduce

Note: This is not a code-specific bug — it's a performance/connectivity regression that affects normal usage. There is no minimal code example, as any request triggers the issue.

1. Install Claude Code VS Code extension (anthropic.claude-code v2.1.167)
2. Sign in with a Claude Pro account
3. Open any project in VS Code (issue reproduced on a small project — no large codebase or heavy indexing involved)
4. Open the Claude Code panel
5. Ensure model is set to Sonnet 4.6 (default)
6. Send any prompt in the chat (e.g., "explain this file" or any simple question)

Expected: Response within normal time (a few seconds).
Actual: One of the following occurs intermittently:

• Request hangs for several minutes before completing
• Request fails with: API Error: Unable to connect to API (ECONNRESET)
• Occasionally completes, but with severely degraded latency

Frequency: Intermittent but persistent — affects the majority of requests over a multi-hour window on Jun 6, 2026.

Environment confirmed clean:

• Network connection verified working (direct API calls return expected 401/404 responses)
• No VPN, proxy, or third-party antivirus active
• Same project, same VS Code, same extension worked normally on previous days
• Behavior persists across multiple extension versions (v2.1.167 and an earlier rollback)
• Behavior persists after VS Code window reload and new chat sessions

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Worked normally until Jun 5, 2026. Started experiencing severe latency and ECONNRESET errors on Jun 6, 2026. Unsure of exact extension version on the last working day, but the issue persists across multiple versions (tested current v2.1.167 and an earlier rollback version — both affected), which suggests the regression may be backend-side rather than extension-side.

Claude Code Version

CLI not installed — using VS Code extension only. Extension version: anthropic.claude-code v2.1.167

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_