[BUG] Claude telling me Fable isn't available when Opus 4.8 or any model is selected

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?

Claude is telling me I can't use Fable 5 when Opus 4.8 or any other model is selected.

What Should Happen?

Should respect the model selected in the model selector.

<img width="990" height="704" alt="Image" src="https://github.com/user-attachments/assets/536acb01-888c-4458-8ddb-45afcf6e58d7" />

Error Messages/Logs

API Error: 400 tools.16.model: Claude Fable 5 is not available. Please use Opus 4.8. Learn more: https://www.anthropic.com/news/fable-mythos-access

Steps to Reproduce

1. Updated Claude to latest osx update when agent paused
2. Restarted Claude
3. Resumed chat I was working on which was started with Opus 4.8
4. Agent tells me Fable 5 is not available
5. Opus 4.8 is active model set (select any model doesn't work)

Have forced quit and restarted.Nothing works. Can't resume agent in this chat.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude 1.13576.0 (1290fc) 2026-06-16T05:46:10.000Z

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_