[BUG] 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?

I'm opening new Claude code window but every request, even the simple ones, will say API Error: 400 due to tool use concurrency issues. So essentially Claude code doesn't work as an extension on VSCODE.

What Should Happen?

Claude Code shouldn't error out and do its tasks.

Error Messages/Logs

API Error: 400 due to tool use concurrency issues.

Steps to Reproduce

in this website, https://static-content.springer.com/esm/art%3A10.1038%2Fs41467-025-67084-x/MediaObjects/41467_2025_67084_MOESM1_ESM.pdf the Supplementary Table 1 shows where the datasets CASSIA benchmarked against was found. Using this information, tell me exactly how I can find the correct versions of the azimuth PBMC human dataset.

Claude: API Error: 400 due to tool use concurrency issues.

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.19

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_