Anthropic: claude-fable-5.1
Claude Fable 5.1 improves on Claude Fable 5 across the board, with the biggest gains in agentic coding, long-running agentic workflows, and knowledge work: long code refactors, front-end and visual code generation, and finance and analysis tasks in particular. It also tends to be more concise than Fable 5 in its plans and summaries. We recommend testing it as a direct upgrade wherever you use Fable 5 today, and alongside Opus 5 on reasoning-heavy tasks.
Inputs used for the providers' own purposes
At least one provider of this model uses your inputs for its own purposes, for example to train AI models. Do not enter personal data of third parties or sensitive data. You can object to this use at any time in your account settings or via "Manage consents" in the chat.
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Supported parameters
All providers = every upstream serving this model supports it. Some providers = depends on which upstream handles the request. Default = the value sent when you leave the parameter unset.
| Parameter | Providers | Default |
|---|---|---|
| include_reasoning | All providers | - |
| max_completion_tokens | Some providers | - |
| max_tokens | All providers | - |
| reasoning | All providers | - |
| reasoning_effort | All providers | - |
| response_format | All providers | - |
| stop | All providers | - |
| structured_outputs | All providers | - |
| tool_choice | All providers | - |
| tools | All providers | - |
| verbosity | All providers | - |