{"name":"claude-fable-5-1","slug":"claude-fable-5-1","family":"model","title":"Models","noun":"model","description":"A claude-fable-5-1 model id is recognized and becomes the fable family default, with UI text updated to Fable 5.1.","description_source":"entry","described_by":{"version":"2.1.257","anchor":"fable-51-model-introduced"},"presence":{"first_seen":null,"removed_in":null,"in_current_build":false,"newest_mined":"2.1.319","builds":0,"mined_builds":159,"first_cited":{"version":"2.1.257","released_at":"2026-09-01 17:15:33","spans":1}},"aliases":[],"entries":[{"version":"2.1.281","anchor":"model-selector-config-always-on-dropped-min-version-bumped","heading":"Model selector config: always_on dropped, min version bumped to 2.1.280","line":"One model entry in the bundled model selector config drops `always_on` thinking and now requires Claude Code 2.1.280 or later","released_at":"2026-09-23 17:01:17","reason":"found in this entry's text"},{"version":"2.1.281","anchor":"bundled-model-selector-sample-defaults-opus-55-to-medium-ef","heading":"Bundled model-selector sample defaults Opus 5.5 to medium effort","line":"Built-in model data now sets Opus 5.5 to medium effort and marks Medium as Default for Opus 5.5 and Fable 5.1","released_at":"2026-09-23 17:01:17","reason":"found in this entry's text"},{"version":"2.1.277","anchor":"model-catalog-version-bump-and-per-surface-model-reassignmen","heading":"Model catalog version bump and per-surface model reassignment","line":"Bundled model catalog updated to version 629 with model reassignments across ccr, ccd, and other surfaces","released_at":"2026-09-18 16:22:26","reason":"found in this entry's text, named in this entry"},{"version":"2.1.263","anchor":"effort-medium-nudge-generalized-to-multiple-models-and-effor","heading":"Effort-medium nudge generalized to multiple models and effort levels","line":"The effort-downgrade nudge now works per model instead of just one, but each model needs its own flag turned on.","released_at":"2026-09-06 02:07:58","reason":"found in this entry's text"},{"version":"2.1.263","anchor":"effort-medium-nudge-generalized-to-per-model-remote-config-g","heading":"Effort-medium nudge generalized to per-model remote-config gates","line":"The effort-downgrade nudge was rebuilt to support multiple models, each hidden behind its own remote switch.","released_at":"2026-09-06 02:07:58","reason":"found in this entry's text"},{"version":"2.1.257","anchor":"fable-51-model-introduced","heading":"Fable 5.1 model introduced","line":"A claude-fable-5-1 model id is recognized and becomes the fable family default, with UI text updated to Fable 5.1.","released_at":"2026-09-01 17:15:33","reason":"found in this entry's text, named in this entry"},{"version":"2.1.257","anchor":"new-model-identity-claude-fable-51-mythos-51","heading":"New model identity: Claude Fable 5.1 \/ Mythos 5.1","line":"A system-prompt identity block describes Claude Fable 5.1 in a Mythos-class tier above Opus, sharing weights with Mythos 5.1.","released_at":"2026-09-01 17:15:33","reason":"found in this entry's text, named in this entry"},{"version":"2.1.257","anchor":"fable-5-branding-shortened-to-fable-in-usage-limit-messa","heading":"'Fable 5' branding shortened to 'Fable' in usage-limit messages","line":"Usage-limit text now says Fable limit, and fable-5-1 and mythos-5-1 aliases were added.","released_at":"2026-09-01 17:15:33","reason":"found in this entry's text"},{"version":"2.1.257","anchor":"claude-fable-5-1-model-wiring-vertex-region-gate","heading":"claude-fable-5-1 model wiring (Vertex region + gate)","line":"claude-fable-5-1 is wired up with its own Vertex region, and fallback lists now gate on a fable51 check.","released_at":"2026-09-01 17:15:33","reason":"found in this entry's text, named in this entry"}],"entries_total":9,"docs":[{"source":"api","path":"about-claude\/model-deprecations","title":"model-deprecations","documented":false},{"source":"api","path":"about-claude\/models\/choosing-a-model","title":"choosing-a-model","documented":false},{"source":"api","path":"agents-and-tools\/agent-skills\/overview","title":"PDF Processing","documented":false},{"source":"api","path":"agents-and-tools\/mcp-connector","title":"mcp-connector","documented":false},{"source":"api","path":"agents-and-tools\/mcp-tunnels\/overview","title":"overview","documented":false},{"source":"api","path":"agents-and-tools\/tool-use\/advisor-tool","title":"advisor-tool","documented":false},{"source":"api","path":"agents-and-tools\/tool-use\/bash-tool","title":"bash-tool","documented":false},{"source":"api","path":"agents-and-tools\/tool-use\/browser-use-sdk","title":"browser-use-sdk","documented":false},{"source":"api","path":"agents-and-tools\/tool-use\/browser-use-tool","title":"browser-use-tool","documented":false},{"source":"api","path":"agents-and-tools\/tool-use\/code-execution-tool","title":"code-execution-tool","documented":false}],"docs_total":12,"gates":[],"related":[{"name":"claude-fable-5","slug":"claude-fable-5","description":"Opus 5 is now the default Opus, with a 1M-context option in the model picker."}],"url":"https:\/\/changelogs.core-directive.com\/reference\/model\/claude-fable-5-1","family_url":"https:\/\/changelogs.core-directive.com\/reference\/model.json"}