[BUG] Persistent 120s API timeout on heavy requests - 24+ hours (March 19-20, 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?

Bug Description

Claude Code API requests consistently hang for 120 seconds then fail with 500 Internal Server Error. This has been ongoing for 24+ hours (since March 19, 2026 ~15:00 KST / 06:00 UTC).

Key observation: Light requests (tool calls, short responses) succeed in 3-7 seconds, but heavy requests (large context + content generation) always timeout at exactly 120 seconds. The server accepts the connection but never completes the response.

Environment

• Claude Code version: 2.1.80
• OS: Windows 11 (WSL2), Docker container (Ubuntu-based)
• Models tested: claude-opus-4-latest, claude-sonnet-4-6 — both fail identically
• Setup: Claude Code inside Docker → claude-code-monitor proxy → https://api.anthropic.com
• Effort levels tested: high, max — no difference

Reproduction

1. Run any Claude Code task that requires significant token generation (e.g., generating SRT subtitle timestamps from a speech analysis file)
2. Request hangs for exactly 120 seconds
3. Fails with: `Error forwarding to anthropic API: failed to forward request: Post

"https://api.anthropic.com/v1/messages?beta=true": context canceled`

What I've Verified

• Not a client-side issue: Direct (non-Docker) Claude Code also experiences extreme slowness (27 minutes for a simple file-read task that normally takes seconds)
• Not a rate limit: No 429 errors. The server accepts connections but hangs silently
• Not model-specific: Both Opus 4.6 and Sonnet 4.6 fail identically
• Not a config issue: Proxy timeouts are set to 10 minutes. The 120s cutoff comes from Claude Code's internal client timeout - Not an auth issue: API key is valid — light requests succeed fine

Expected Behavior

• Heavy requests should complete within a reasonable time, OR
• The server should return a proper 429/529 error immediately instead of accepting the connection and hanging for

120 seconds

Impact

All content-generation workflows are completely blocked. Only trivial tool-call responses work. This effectively makes Claude Code unusable for any real task.

Related Issues

• #35508 — March 17, Windows 500 errors
• #35484 — Persistent 500 across all models
• #28624 — Intermittent 500 on Opus 4.6
• anthropics/claude-code-action#1079 — OIDC 500 since March 18

What Should Happen?

Expected Behavior

• Heavy requests should complete within a reasonable time, OR
• The server should return a proper 429/529 error immediately instead of accepting the connection and hanging for

120 seconds

Error Messages/Logs

## Proxy Logs (UTC)
Pattern: light requests succeed, heavy requests always timeout                                                        
2026/03/20 12:29:05 POST /v1/messages 500 Internal Server Error (120.00s)  ← heavy
2026/03/20 12:29:06 POST /v1/messages 200 OK (3.21s)  ← light
2026/03/20 12:29:12 POST /v1/messages 200 OK (4.91s)  ← light                                 
2026/03/20 12:29:19 POST /v1/messages 200 OK (7.25s)  ← light                                 
2026/03/20 12:31:06 POST /v1/messages 500 Internal Server Error (120.00s)  ← heavy
2026/03/20 12:33:08 POST /v1/messages 500 Internal Server Error (120.00s)  ← heavy                                 

This pattern has repeated every ~2 minutes for 24+ hours

Occasionally a streaming response starts but dies at 300s:                                                            

2026/03/20 12:25:05 Streaming error: context deadline exceeded (300.19s)

Steps to Reproduce

Reproduction

1. Run any Claude Code task that requires significant token generation (e.g., generating SRT subtitle timestamps from a speech analysis file)
2. Request hangs for exactly 120 seconds
3. Fails with: `Error forwarding to anthropic API: failed to forward request: Post

"https://api.anthropic.com/v1/messages?beta=true": context canceled`

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.80

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

WSL (Windows Subsystem for Linux)

Additional Information

_No response_