Automatic migration of claude-fable-5 model alias to fable

If your model setting says claude-fable-5, startup rewrites it to the fable alias automatically.

Read from

Names in the bundleclaude-fable-5fable

Since it was published

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 since 11 Sep 2026 A small documentation edit on Or, for the model with the same capabilities and no access approval requirement: touched a line naming claude-fable-5 after this was published. * If you replay conversation history on an earlier model, strip `thinking` and `redacted_thinking` blocks from prior assistant turns first. Thinking blocks from `claude-fable-5` and `claude-mythos-5` are readable only by the model that pro… models/fable-5/migration-guide see the edit

Added since 10 Sep 2026 A small documentation edit on Escalate hard decisions with the advisor tool touched a line naming fable after this was published. Fable 5.1 requires Claude Code v2.1.257 or later. Both Fable models require [Fable access](/docs/en/model-config#work-with-fable). advisor see the edit

Confirmed since 10 Sep 2026 Anthropic's documentation has since written up fable, on Create Session. - `BetaManagedAgentsModel = "claude-fable-5-1" or "claude-sonnet-5" or "claude-fable-5" or 11 more or string` api/beta/sessions/create see the edit

Confirmed since 10 Sep 2026 Anthropic's documentation has since written up claude-fable-5, on Create Session. - `BetaManagedAgentsModel = "claude-fable-5-1" or "claude-sonnet-5" or "claude-fable-5" or 11 more or string` api/beta/sessions/create see the edit

How sure we are

One source agreesOne thing we can check says the same as this entry.

Anthropic's documentation agreesAnthropic's documentation has since written up claude-fable-5, on Create Session.

See this entry in the whole of v2.1.257 →