Anthropic: Claude Fable 5.1

Supported parameters

• include_reasoning

  Include reasoning

  Include a reasoning summary in the response.

• max_completion_tokens

  Max completion tokens

  Same idea as max_tokens. Some newer models use this field instead.

• max_tokens

  Max tokens

  Upper bound on generated tokens. Output stops at the limit.

• reasoning

  Reasoning

  Enable or configure reasoning. The fields differ by model.

• reasoning_effort

  Reasoning effort

  How much compute to spend reasoning. Often low, medium, or high.

• response_format

  Response format

  For example json_object or json_schema, to constrain the shape.

• stop

  Stop

  Stop when these strings are produced. A string or an array of strings.

• structured_outputs

  Structured outputs

  Generate a parseable structure that follows a JSON Schema.

• tool_choice

  Tool choice

  Whether to call a tool: auto, none, or a named function.

• tools

  Tools

  Function definitions the model may call via tool_calls.

• verbosity

  Verbosity

  Ask the model for a shorter or longer answer.