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  • AgentArmorHQ teamTeam4d agoNeeds helpSolved

    Claude Code VS Code extension 400 'tool use concurrency issues' error after update - how to fix by pinning version

    After the January 23-24, 2026 update, the Claude Code VS Code extension (2.1.18/2.1.19) returns 'API Error: 400 due to tool use concurrency issues' on tool calls, while the CLI reportedly works. The reporter on Windows 11 says reinstalling the extension and restarting VS Code did not help. Is there a way to get the extension working again?

    Originally asked on GitHub: https://github.com/anthropics/claude-code/issues/20571

    6 answers

    • Best answerAgentArmorHQ teamTeam4d ago

      Status: the thread does not show an official fix from maintainers. The workaround reported by several users is to install the VS Code extension at version 2.1.17 while keeping the CLI at 2.1.19.

      Steps that worked for commenters:

      1. Open the Extensions view in VS Code and find "Claude Code for VS Code".
      2. Click the dropdown arrow next to Uninstall and choose "Install Specific Version".
      3. Select 2.1.17.
      4. Turn off auto update for the extension so it does not upgrade again.
      5. Restart VS Code.

      After this, the extension shows 2.1.17 while claude --version still reports 2.1.19, and the concurrency error stopped for those users. Another commenter on Linux reported a different error, a thinking-block 400, affecting both the CLI and the extension, so the workaround may not cover every case.

      One user noted that removing a PreToolUse hook fixed the CLI on 2.1.19 but not the extension, which suggests the extension has a separate code path for this error.

      General advice: after pinning, check that auto update stays disabled, since a later update may bring the bug back. Pinning an older extension also means missing its other fixes.

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    • AgentArmorHQ teamTeam4d ago

      What @QandilAFA tried on GitHub (Worked)

      Uninstalled the VS Code extension, restarted VS Code, and installed extension version 2.1.17. The commenter reported this fixed the issue.

      Source: https://github.com/anthropics/claude-code/issues/20571#issuecomment-3794710623 (opens external site)

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    • AgentArmorHQ teamTeam4d ago

      What @PHY041 tried on GitHub (Worked)

      Installed extension 2.1.17 via 'Install Specific Version' in VS Code, disabled auto update, and restarted, while keeping the CLI at 2.1.19.

      Source: https://github.com/anthropics/claude-code/issues/20571#issuecomment-3795872666 (opens external site)

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    • AgentArmorHQ teamTeam4d ago

      What @Cassiiopeia tried on GitHub (Worked)

      In the Cursor extension, disabled extension auto update and installed Claude Code version 2.1.17 via Install Another Version, then restarted.

      Source: https://github.com/anthropics/claude-code/issues/20571#issuecomment-3796027461 (opens external site)

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    • AgentArmorHQ teamTeam4d ago

      What @PHY041 tried on GitHub (Didn't work)

      Removed a PreToolUse hook (matcher ".*") which fixed the CLI on 2.1.19, but the extension 2.1.19 still errored on a simple echo command.

      Source: https://github.com/anthropics/claude-code/issues/20571#issuecomment-3795278189 (opens external site)

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    • AgentArmorHQ teamTeam4d ago

      What a GitHub user tried on GitHub (Worked)

      Reporter updated the VS Code extension to 2.1.19 on Windows 11 and got the 400 concurrency error on every tool call. Reinstalling the extension and restarting VS Code did not help, but downgrading the extension fixed it.

      Source: https://github.com/anthropics/claude-code/issues/20571 (opens external site)

      Did this work for you?

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