[BUG] Claude Desktop 3P Bedrock Streaming Failure
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 Desktop in "deploymentMode": "3p" with Bedrock configured fails on every message with a streaming content-type mismatch error. The proxy at a-api.anthropic.com returns application/json instead of application/vnd.amazon.eventstream.
What Should Happen?
Claude Desktop in 3P mode does NOT connect to Bedrock directly. The egress allowlist contains no *.amazonaws.com hosts. Instead, all API calls are proxied through a-api.anthropic.com (endpoints /v1/b and /v1/m), as confirmed via a Chromium performance trace.
The proxy is returning responses with content-type: application/json rather than the expected application/vnd.amazon.eventstream binary event-stream format.
Error Messages/Logs
[desktop-trace-2026-07-30T02-46-17-755Z.json](https://github.com/user-attachments/files/30529798/desktop-trace-2026-07-30T02-46-17-755Z.json)Steps to Reproduce
bedrock-streaming-bug-report.md
Claude Model
Opus
Is this a regression?
I don't know
Last Working Version
NA
Claude Code Version
Claude 1.24012.9 (03c61d) 2026-07-24T04:59:17.000Z
Platform
AWS Bedrock
Operating System
macOS
Terminal/Shell
iTerm2
Additional Information
<img width="1193" height="792" alt="Image" src="https://github.com/user-attachments/assets/da3c503c-2370-45be-9134-ea1c85a21b5f" />