Claude Mythos 5.1

Claude Mythos 5.1 is the same underlying model as Fable 5.1 — identical weights, identical pricing — running with more permissive safeguards in cybersecurity and the life sciences. It is invitation-only, not a consumer product.

Best for

• Defensive cybersecurity work at vetted organisations
• Bioinformatics, protein design and organic chemistry research
• Anything where Fable 5.1's production safeguards block legitimate work

How it compares — and the India angle

• Access runs through Anthropic's trusted-access programmes — the Cyber Verification Program and the Life Sciences Verification Program — currently limited to US organisations, so most readers cannot get it and do not need it.
• The capability gap in the benchmark tables is the safeguards, not the model: 60.9% vs Fable 5.1's 55.8% on Terminal-Bench 4.0, on identical weights.
• It also powers Claude Security, which scans codebases for vulnerabilities and is available to all Claude Enterprise customers — that is the route most teams will actually meet this model through.