{"version":"2.1.257","anchor":"new-model-identity-claude-fable-51-mythos-51","canonical_anchor":"new-model-identity-claude-fable-51-mythos-51","heading":"New model identity: Claude Fable 5.1 \/ Mythos 5.1","tier":"soon","area":"Models","scope":null,"heads_up":null,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.257\/e\/new-model-identity-claude-fable-51-mythos-51","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.257","markdown":"### New model identity: Claude Fable 5.1 \/ Mythos 5.1\n\nA system-prompt identity block describes Claude Fable 5.1 in a Mythos-class tier above Opus, sharing weights with Mythos 5.1.\n\nA new system-prompt identity block describes 'Claude Fable 5.1' as the newest model in Anthropic's Claude 5 family, placed in the Mythos-class tier above Opus. It shares weights with 'Claude Mythos 5.1', an unrestricted variant available only to approved organizations, and is selected when the model id resolves to `claude-fable-5-1`.\n\n- Area: Models\n- Names: `claude-fable-5-1`\n- Tier: Nothing to try yet\n- Useful: 5\/5\n- Signal: 5\/5\n- Present in the build but not switched on"}