[BUG] All models fail with ConnectionRefused while the same OAuth token reaches the API (macOS, 2.1.219–2.1.220)

Preflight Checklist

• [x] I searched existing issues. The closest reports I found are #53346 and #48008, but neither includes the isolation results below.
• [x] This is a single bug report.
• [x] I am using the latest Claude Code release.

What's Wrong?

Every first-party /v1/messages request fails almost immediately with a generic Connection error. After all 11 retries, Claude Code reports ConnectionRefused.

This affects both the main inference request and session-title generation. Failing requests do not show an x-client-request-id in the debug log and record api=0ms, suggesting the failure happens before Claude Code receives an API response or starts a stream.

The same OAuth access token is accepted by api.anthropic.com when tested directly with a deliberately incomplete request: the API returns a normal HTTP 400 validation response (model: Field required) and a request ID. This isolates the problem to Claude Code's request/transport path rather than DNS, TLS, basic API reachability, or token validity.

The failure is deterministic right now, but the same Claude Code version successfully streamed a response on the previous day after an earlier period of identical failures.

What Should Happen?

Claude Code should send the authenticated request and either begin streaming or return the actual HTTP/API error. It should not classify a reachable API and accepted OAuth credential as ConnectionRefused.

If a local preflight, request construction, beta/header validation, or transport initialization step fails, the debug log should expose that underlying error instead of the generic connection classification.

Error Messages/Logs

Final retry:

[DEBUG] [API REQUEST] /v1/messages source=repl_main_thread
[ERROR] API error (attempt 11/11): undefined Connection error.
[ERROR] Error in API request: Connection error.
[ERROR] Connection error details: code=ConnectionRefused, message=Unable to connect. Is the computer able to access the url?
[ERROR] API connection_error after retries: Connection error.
[DEBUG] [engine] turn 1 end (turns=1 usage in=0 out=0 cost=$0.0000 api=0ms stop=stop_sequence resultLen=0)

The first attempt typically fails within 1–5 ms:

[DEBUG] [API:timing] dispatching to firstParty model=claude-haiku-4-5-20251001
[DEBUG] [API REQUEST] /v1/messages source=sdk
[ERROR] API error (attempt 1/11): undefined Connection error.

A successful session using the same installed 2.1.220 binary on the previous day logged:

[DEBUG] [API REQUEST] /v1/messages x-client-request-id=<uuid> source=repl_main_thread
[DEBUG] Stream started - received first chunk
[DEBUG] [API:timing] first byte after 1378ms

Isolation / Tests Performed

| Test | Result |
|---|---|
| claude doctor | Native 2.1.220, darwin-arm64, no installation issues found |
| claude auth status | Logged in via claude.ai, provider firstParty, Max subscription |
| OAuth credential metadata | Access token is unexpired and includes user:inference scope |
| Direct unauthenticated POST to https://api.anthropic.com/v1/messages | HTTP 401 as expected |
| Node fetch() to the same endpoint without auth | HTTP 401 as expected |
| Direct POST using the same OAuth access token and {} body | HTTP 400 invalid_request_error: model: Field required; request ID req_011CdZS1XGNn1eAW9gGJum1B |
| TLS verification | Passes; curl ssl_verify_result=0 |
| Proxy-related environment | HTTP_PROXY, HTTPS_PROXY, and NO_PROXY are unset |
| claude --safe-mode -p ... | Same repeated Connection error; rules out hooks, plugins, skills, LSP, and MCP customization |
| --no-session-persistence --tools '' --effort low | Same failure with a minimal client configuration |
| Model: Claude Sonnet 5 | Fails |
| Model: claude-haiku-4-5-20251001 | Fails |
| Native Claude Code 2.1.220 | Fails |
| pnpm dlx @anthropic-ai/claude-code@2.1.220 | Fails |
| pnpm dlx @anthropic-ai/claude-code@2.1.219 | Fails |
| Anthropic status API at test time | All systems operational; zero unresolved incidents |

A socket observation during the failing run showed established TLS connections to Anthropic's edge, while Claude Code still classified each request as ConnectionRefused.

Steps to Reproduce

1. Sign in with a Claude Max subscription using claude auth login.
2. Run:

timeout 30 claude \
  --safe-mode \
  --no-session-persistence \
  --model haiku \
  --effort low \
  --tools '' \
  --debug-file /tmp/claude-safe-mode.log \
  -p 'Reply exactly OK.'

1. Observe that the command eventually prints Execution error.
2. Inspect /tmp/claude-safe-mode.log.
3. Each /v1/messages attempt fails immediately with undefined Connection error.
4. Let all retries complete; the final classification is ConnectionRefused.

Claude Model

Multiple models: Claude Sonnet 5 and Claude Haiku 4.5

Is this a regression?

Intermittent regression. Claude Code 2.1.220 successfully completed requests on 2026-07-30, but the same version fails consistently on 2026-07-31. Version 2.1.219 currently fails as well.

Last Working Version

2.1.220 (worked on the previous day with the same account and machine)

Claude Code Version

2.1.220 (native, commit 4073f59596e2); also reproduced with 2.1.219

Platform

Anthropic API / first-party Claude.ai OAuth

Operating System

macOS 26.5 (Build 25F71), Apple Silicon arm64

Terminal/Shell

Ghostty 1.3.1 / zsh

Additional Information

• No API key or custom ANTHROPIC_BASE_URL is configured.
• No proxy environment is configured.
• The official status page had no active incident during testing.
• I can provide the full sanitized debug logs privately if needed.
• Related: #53346 (ConnectionRefused) and #48008 (stream connection failures where curl still succeeds).