Claude Code v2.1.37 Fast Mode Bug Fix — 3 Things to Know [2026]

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Claude Code v2.1.37 Update: Key Takeaways

  • Fixed a bug where /fast wasn’t immediately applied after enabling /extra-usage in Fast mode.
  • Follow-up patch to the Opus 4.6 Fast mode introduced in v2.1.36.
  • Focus on improving developer workflow stability.

Fast Mode Bug: What Exactly Was It?

Anthropic released Claude Code v2.1.37 on February 7th. This update is a patch focused on a single bug fix.[GitHub Release]

It fixed an issue where the /fast command wouldn’t work immediately after activating /extra-usage. Fast mode is a new feature added for Opus 4.6 in v2.1.36.[v2.1.36 Release]

Recent Updates Are Coming in Hot

Eight versions, from v2.1.30 to v2.1.37, have been released in just 5 days. Opus 4.6 and agent team features were added in v2.1.32, and a sandbox security vulnerability was patched in v2.1.34.[Claude Code Releases]

It seems Anthropic is pushing Claude Code to become a terminal-based AI development platform. It currently has over 65,000 stars on GitHub.[GitHub Repository]

How to Apply the Update

Just re-run the installation script, or if you’re a Homebrew user, update with brew upgrade. If you’re using Fast mode, we recommend checking if /fast works immediately after switching /extra-usage.

Frequently Asked Questions (FAQ)

Q: What is Claude Code Fast Mode?

A: It’s a feature introduced in v2.1.36. It increases the response speed in the Opus 4.6 model, making it suitable for simple tasks. It’s activated with the /fast command, allowing users to choose between cost and speed.

Q: What is Extra Usage?

A: It’s a feature that allows you to continue using Claude Code even after exceeding the basic usage allowance. You can turn it on and off with the /extra-usage command. This patch ensures Fast mode is applied immediately after activation.

Q: How do I update to the latest version?

A: For macOS and Linux, re-run the installation script. For Homebrew, use brew upgrade, and for Windows, use winget upgrade Anthropic.ClaudeCode. NPM installation is no longer recommended.

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