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

# tool_choice_required_not_supported

> HTTP 400 — Model does not support tool_choice="required".

## HTTP status

`400 invalid_request_error`

## Typical cause

The request sets `tool_choice: "required"` but the selected model doesn't reliably guarantee a tool call in the response. Auriko rejects this combination to prevent silent failures in agentic pipelines.

## Resolution

Use `tool_choice: "auto"` instead. Models still call tools when prompted appropriately. Alternatively, remove any provider constraint to allow routing to a capable provider.