## Description Intermittent 'API Error: 400 due to tool use concurrency issues' appears in VSCode extension, even on simple single-tool operations like Read. ## Environment - OS: Windows 11 - IDE: VSCode with Claude Code extension - Date: January 2025 ## Behavior - Error appears even on simple Read operations (single tool, no parallelism) - The operation often **succeeds** despite the error message being displayed - Happens intermittently, even after PC restart - Not limited to print mode (-p)

## ✅ WORKAROUND FOUND **The fix:** Install VS Code extension version **2.1.17** while keeping CLI at **2.1.19** **Steps:** 1. In VS Code Extensions → "Claude Code for VS Code" 2. Click dropdown next to Uninstall → "Install Specific Version" → **2.1.17** 3. Uncheck "Auto Update" 4. Restart VS Code **Result:** Extension 2.1.17 + CLI 2.1.19 = ✅ Works The bug is in the VS Code extension code (2.1.18/2.1.19), not the CLI or API.

[BUG] API Error 400 'tool use concurrency issues' in VSCode extension on simple operations

Status Fixed / completed

Maintainer reply None cached

Workaround ✓ Mentioned in thread ↓

Activity 9 comments · opened Jan 24, 2026 · closed Feb 6, 2026

Description

Intermittent 'API Error: 400 due to tool use concurrency issues' appears in VSCode extension, even on simple single-tool operations like Read.

Environment

OS: Windows 11
IDE: VSCode with Claude Code extension
Date: January 2025

Behavior

Error appears even on simple Read operations (single tool, no parallelism)
The operation often succeeds despite the error message being displayed
Happens intermittently, even after PC restart
Not limited to print mode (-p), occurs in interactive VSCode extension

Related Issues

#18130 (locked) - Similar issue in print mode
#9438 (locked) - Same error with non-existent /rewind suggestion

Expected Behavior

No error should be displayed when the tool operation succeeds.

Actual Behavior

Error message 'API Error: 400 due to tool use concurrency issues' is shown even though the tool result is received correctly. This appears to be a display/UI bug rather than an actual failure.

View original on GitHub ↗

9 Comments

github-actions[bot] · 7 months ago

Found 3 possible duplicate issues:

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🤖 Generated with Claude Code

PnoT · 7 months ago

EDIT: I rolled back to the 2.1.17 version of the extension, and things are working again for now. fingers crossed.

I'm having the same issue with simple commands in VS Code with the latest extension.

gantamk · 7 months ago

EDIT: I rolled back to the 2.1.17 version of the extension, and things are working again for now. _fingers crossed_. I'm having the same issue with simple commands in VS Code with the latest extension.

Thanks, that worked for me as well.

Lerner98 · 7 months ago

Confirmed: Downgrading VS Code extension to 2.1.17 fixes the issue. The bug was introduced in version 2.1.19.

TrentBrown · 7 months ago

Downgrading worked for me too. Thanks y'all.

AltyorNG · 7 months ago

Thank you for your advice.

jervaise · 7 months ago

Downgrading works (remember to restart)

PHY041 · 7 months ago

✅ WORKAROUND FOUND

The fix: Install VS Code extension version 2.1.17 while keeping CLI at 2.1.19

Steps:

In VS Code Extensions → "Claude Code for VS Code"
Click dropdown next to Uninstall → "Install Specific Version" → 2.1.17
Uncheck "Auto Update"
Restart VS Code

Result: Extension 2.1.17 + CLI 2.1.19 = ✅ Works

The bug is in the VS Code extension code (2.1.18/2.1.19), not the CLI or API.

github-actions[bot] · 6 months ago

This issue has been automatically locked since it was closed and has not had any activity for 7 days. If you're experiencing a similar issue, please file a new issue and reference this one if it's relevant.