Nothing to try yetTier: how much it should matter to you
4Useful: my rating, 1 to 5
4Signal: worth watching, 1 to 5
ModelsArea: what it touches
In DevelopmentKind: in v2.1.257,
What probably matters to youSection of the release
A new model id claude-fable-5-1 and its Vertex region constant VERTEX_REGION_CLAUDE_FABLE_5_1 were added. The opus/haiku fallback-list builders now check feature gate fable51 (replacing the previous fable5 check) before appending the model via WZe().
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Added sinceA small documentation edit on Models overview touched a line naming claude-fable-5-1 after this was published.| [Claude Platform on AWS ID](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws) | `claude-fable-5-1` | `claude-opus-5` | `claude-sonnet-5` | `claude-haiku-4-5` |models/overviewsee the edit
Confirmed sinceAnthropic's documentation has since written up claude-fable-5-1, on Create Session.- `BetaManagedAgentsModel = "claude-fable-5-1" or "claude-sonnet-5" or "claude-fable-5" or 11 more or string`api/beta/sessions/createsee the edit
How sure we are
Two sources agreeTwo things we can check say the same as this entry.
Anthropic's documentation agreesAnthropic's documentation has since written up claude-fable-5-1, on Create Session.
Anthropic's release notes agreeAdded Claude Fable 5.1 (claude-fable-5-1), now the default Fable model — 1M context, $10/$50 per Mtok with $0.25/Mtok cache reads
