Claude Desktop 3P mode — inferenceCustomHeaders not applied to HTTP requests

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?

• App version: 1.9255.2 / Claude Code VM 2.1.149.0d3
• Mode: Third-party inference (custom-3p, provider: gateway)
• Symptom: 401 from APIM gateway — Ocp-Apim-Subscription-Key header set in

inferenceCustomHeaders is not sent with API requests

cowork_host_loop_debug.log

What Should Happen?

It was able to connect without issues.

Error Messages/Logs

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Failed to authenticate. API Error: 401 Access denied due to missing subscription key. Make sure to include subscription key when making requests to an API.
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Steps to Reproduce

Configure a gateway with inferenceCustomHeaders containing
Ocp-Apim-Subscription-Key — the header is ignored

• Not an infra issue: Same request via curl with the header works perfectly

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

previous version

Claude Code Version

Claude 1.9255.2 (1dc8f7) 2026-05-27T01:57:20.000Z

Platform

Other

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_