[Bug] Unexpected model downgrade from Claude Fable 5 to Claude Opus 4.8

Question

**Bug Description**
I got switched to Opus from Fable, but I am simply doing AI safety research on emergent misalignment, personas and alignment training.

**Environment Info**
- Platform: darwin
- Terminal: vscode
- Version: 2.1.197
- Feedback ID: 01912fc2-e9e4-42a7-b3fe-85c283d2a905

**Errors**
```json
[]
```