Usage creeping up unexpectedly while idle; session reports unfamiliar model "Fable" (claude-fable-5[1m])

Environment

• Claude Code version: 2.1.170
• Platform: macOS (Darwin 25.5.0)
• Terminal: zsh

Description

Two possibly related observations:

1. Unfamiliar model: My session reports it is powered by a model named "Fable 5" with model ID claude-fable-5[1m]. I did not select this model and don't see it documented anywhere. I expected to be on a standard Opus/Sonnet model.

1. Usage creeping up: My usage (as shown in /usage) keeps increasing at times when I don't believe I'm actively running anything — no prompts in flight, no background tasks I'm aware of. It appears to creep up on its own.

Steps to reproduce

1. Open a Claude Code session
2. Check /usage periodically while idle
3. Observe usage increasing without active prompting
4. Model reported by the session is claude-fable-5[1m]

Expected behavior

• Usage should only increase from work I initiate (or clearly attributable background features)
• The active model should be one I selected or a documented default

Actual behavior

• Usage increases at seemingly random times
• Session is on an undocumented "Fable" model

Happy to provide logs or session IDs if useful.