Claude Fable is not “slightly more expensive” — it’s a premium tier.
API pricing per 1M tokens:
Fable: $10 input / $50 output
Opus: $5 input / $25 output
Sonnet: $3 input / $15 output
So Fable is 2× Opus and about 3.33× Sonnet. For most coding/finance/reporting workflows, Sonnet still feels like the default; Opus for hard tasks; Fable only when it materially reduces turns or rework.