Claude Fable 5 shares Opus training cutoff

Anthropic's decision to use the same training cutoff for Fable 5 and the Opus line proves that model tier differentiation is achieved via architectural and post-training enhancements rather than newer data. Sharing the exact same knowledge cutoff ensures consistent outputs across both models, especially since Fable 5 falls back to Opus 4.8 when safety classifiers are triggered. This dataset consistency highlights Anthropic's ability to reuse a preprocessed corpus across multiple model lines. However, it also means both model lines remain equally limited when addressing current events updated after January 2026.