> ## Documentation Index
> Fetch the complete documentation index at: https://docs.narrative.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Forced Tool Choice Not Supported

> The model does not accept a forced tool call.

**HTTP status:** 400

## Error message

```text theme={null}
model '{model}' does not support tool_choice.specific_tool ('{tool}'); use tool_choice.auto and ask for the tool in the prompt
```

```text theme={null}
model '{model}' does not support tool_choice.any; use tool_choice.auto and ask for the tool in the prompt
```

## When this error occurs

The run sent a `tool_choice` that forces a tool call, `{"kind":"any"}` or `{"kind":"specific_tool"}`, to a model
that doesn't accept one. Claude Sonnet 5.5 (`anthropic.claude-sonnet-5.5`) and Claude Opus 5.5 (`anthropic.claude-opus-5.5`) are such models: they always decide for themselves
whether to call a tool.

## How to fix

Use `tool_choice: {"kind":"auto"}`, or leave `tool_choice` out. The model still sees every tool you declared. If you
need a particular tool called, say so in the message, for example "Use the `confirm_booking` tool." To keep a forced
call, run the conversation on a model that accepts one, such as `anthropic.claude-opus-5.0`.

## Not affected

Structured output (`output_format_schema`) works on these models. The platform asks for the answer without forcing a
tool, and retries if the model doesn't give one.