Model launch and safety guide · Anthropic · Advanced
You want Anthropic's September 1, 2026 model announcement covering Fable 5.1 for general availability and Mythos 5.1 for trusted-access research use.
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Model docs · Anthropic · Intermediate to advanced
You need Anthropic's September 1, 2026 source of truth for Claude Fable 5.1 and invite-only Mythos 5.1, including model IDs, pricing, availability, long-horizon agent strengths, and breaking changes from Fable 5.
anthropic, claude fable 5.1, claude mythos 5.1, frontier models, model selection