
CONFIRMEDLAB
Same weights, two safeguard levels
Confirmed Sep 2026 on Anthropic’s site: same underlying model, different safeguard levels. Fable is generally available; Mythos is trusted-access only.
1 Sep 2026 · anthropic.com
- Anthropic introduced Claude Fable 5.1 and Claude Mythos 5.1 as its most advanced models for coding and knowledge work, with research capabilities highlighted on the same page.
- Anthropic states they are the same model with different safeguard levels: Fable 5.1 generally available; Mythos 5.1 only through trusted access programs aimed at cybersecurity and life sciences work.
Why it mattersSplit-safeguard twins are becoming a product pattern: one public SKU, one gated SKU.
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