When Claude Code starts, it now checks your saved model setting. If it is claude-fable-5-1 or claude-fable-5-1[1m], Claude Code changes it to the fable alias. An alias is a short name that always points to the current Fable model rather than one fixed version. A similar startup step used to do this for claude-fable-5.
The move is skipped when:
- you use a third-party provider, set either through environment variables or through how you sign in
- the
fablealias is not allowed for you
Team and enterprise organisations get a second, delayed move. It waits until the organisation is entitled to the fable alias, gives up after 14 days, and does nothing at all after 15 December 2026. This delayed move is on by default in the code unless it is switched off remotely.
If you pinned Fable 5.1 on purpose, your choice is changed without a prompt and will follow the alias from then on. Check your model setting if you want to stay on a specific version.
tengu_amber_thistle Not enough to sayNothing here resolved what this flag was doing on this version, so nothing here should be read as on or off.
This account: no value returned · anonymous baseline: no value returned · compiled default in v2.1.321: on
These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.
Read once, for one account on one subscription tier, against v2.1.321. It isn't a statement about your account. What a flag value here can and cannot tell you
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.
7. **Pass thinking blocks back unchanged and keep history append-only:** Append each assistant turn exactly as the API returned it, thinking blocks included. On Claude Fable 5.2, Claude Mythos 5.2, Claude Fable 5.1, Claude Mythos 5.1, Clau…build-with-claude/prompt-engineering/claude-prompting-best-practices see the edit
| Beta | Claude API, [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws) | [Claude Fable 5.2](https://platform.claude.com/docs/en/models/fable-5-2/overview), [Claude Mythos 5.2](https://pl…build-with-claude/compaction-threshold see the edit
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A small documentation edit on claude-tag touched a line naming fable after this was published.
New in this build: tengu_amber_thistle