[BUG] Visual Studio Code: API Error: 400 due to tool use concurrency issues.

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?

When I instruct the visual studio code extension to perform any action, it returns a 400 error after each and every step. Even when I follow the support instructions and use a prompt that explains that I do not want to use parallel tool invocations, it still fails. See the attached screenshot for the latest example.

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What Should Happen?

Claude should perform the action without failing on API Error: 400 due to tool use concurrency issues.

Error Messages/Logs

Steps to Reproduce

Open a project in visual studio code
instruct Claude to perform an action
watch it fail after completing the first step

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

I'm powered by Claude Opus 4.5 (model ID: claude-opus-4-5-20251101). This is the most recent frontier Claude model from Anthropic, with a knowledge cutoff of May 2025.

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_