[BUG] ECONNRESET on every API call — macOS 26.3.1 Tahoe, Intel x86_64

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?

Claude Code v2.1.83 fails with ECONNRESET on every API call, including /init, claude -p "hello", and background telemetry. The native binary's bundled Bun HTTP client cannot establish connections to api.anthropic.com, despite the network being fully functional. Standalone Bun (installed via npm), Node.js, and curl all connect to the API successfully from the same machine, confirming the issue is specific to Claude Code's internal HTTP client configuration — not the Bun runtime or the network.

What Should Happen?

Claude Code should connect to the Anthropic API and respond to prompts normally, the same way curl, Node.js, and standalone Bun do on this system.

Error Messages/Logs

❯ /init
  ⎿  API Error: Unable to connect to API (ECONNRESET)

Debug log (key lines):
[DEBUG] CA certs: useSystemCA=false, extraCertsPath=undefined
[ERROR] API error (attempt 1/11): undefined Connection error.
[ERROR] API error (attempt 2/11): undefined Connection error.
[ERROR] API error (attempt 3/11): undefined Connection error.
...
[ERROR] 1P event logging: 39 events failed to export (code=ECONNRESET, The socket connection was closed unexpectedly.)
[ERROR] 1P event logging: 33 events failed to export (code=ECONNRESET, The socket connection was closed unexpectedly.)

MCP servers also fail to authenticate during startup:
[ERROR] MCP server "claude.ai Google Calendar" Error: Streamable HTTP error: {"type":"error","error":{"type":"authentication_error","message":"MCP server requires authentication but no OAuth token is configured."}}
[ERROR] MCP server "claude.ai Gmail" Error: Streamable HTTP error: {"type":"error","error":{"type":"authentication_error","message":"MCP server requires authentication but no OAuth token is configured."}}

Steps to Reproduce

1. Use an Intel Mac running macOS 26.3.1 (Tahoe), build 25D771280a
2. Install Claude Code v2.1.83 (native binary)
3. Launch claude and run /init — fails with ECONNRESET
4. Try claude -p "hello" — hangs, then fails with ECONNRESET

Confirm network works with all other tools:
curl -v --ipv6 https://api.anthropic.com -m 10 → 404 (success)
curl -s https://api.anthropic.com/v1/messages -o /dev/null -w "%{http_code}" → 405 (success)
node -e "const https = require('https'); const req = https.request('https://api.anthropic.com/v1/messages', {method: 'POST'}, (res) => { console.log('Status:', res.statusCode); res.on('data', () => {}); }); req.on('error', (e) => console.log('Error:', e.message)); req.end();" → 401 (success)
bun -e "fetch('https://api.anthropic.com/v1/messages', {method: 'POST'}).then(r => console.log(r.status)).catch(e => console.log(e))" → 401 (success)

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

v2.1.83

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

macOS 26.3.1 (Tahoe), Intel x86_64, build 25D771280a
Claude Code v2.1.83, native binary (Mach-O 64-bit x86_64 with bundled Bun)
Node.js v22.18.0
No proxy, no VPN, no system extensions (systemextensionsctl list → 0 extensions)
Auth: Claude Pro account via OAuth (confirmed working via /status)
Binary at ~/.local/bin/claude is a self-contained Mach-O with embedded __BUN segment
npm-installed version also fails because it delegates to the same native binary
Attempted fixes that did not help:

CLAUDE_CODE_USE_SYSTEM_CA=1
NODE_EXTRA_CA_CERTS=/etc/ssl/cert.pem
CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC=1
Full cache clear (rm -rf ~/.claude)
pkill -9 -f claude and clean restart

Related issues: #5674, #13657, #25229, #29591, #35768, #37077