[BUG] /effort command returns "Unknown skill: effort" despite being documented

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?

The /effort command is documented on Claude's official blog and docs but returns "Unknown skill: effort" when used in Claude Code v2.1.12.

Running /effort or /effort high both fail with the same error message.

The feature is referenced in:

• https://claude.com/blog/claude-model-and-effort-level-in-claude-code
• https://platform.claude.com/docs/en/build-with-claude/effort
• https://code.claude.com/docs/en/model-config

What Should Happen?

The /effort command should either:

1. Open an interactive slider to set thinking effort level (as documented)
2. Accept a level argument like /effort high to set effort directly

Or if the feature isn't available yet, it should not be in public documentation.

Error Messages/Logs

"Unknown skill: effort"

Steps to Reproduce

1. Install Claude Code via npm: npm install -g @anthropic-ai/claude-code
2. Verify version: claude --version → 2.1.12
3. Start a session: claude
4. Run /effort
5. Observe error: "Unknown skill: effort"

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Unknown

Claude Code Version

2.1.12

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Same issue -> https://github.com/anthropics/claude-code/issues/33000