Claude Fable 5 changelog

New Fable 5 safety classifier flags more benign coding requests

To redeploy Fable 5, Anthropic trained a stricter cyber classifier that blocks the reported bypass in over 99% of cases. Anthropic says it also flags benign requests more often during routine coding and debugging, and blocked requests go to Opus 4.8.

Who is affected:

Developers using Fable 5 for coding and debugging.

What to do:

Expect occasional fallbacks to Opus 4.8. Consider Opus 5 for security-adjacent code.