> ## 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.

# input_requires_responses_endpoint

> HTTP 400 — Request input contains types served only via the native Response API, and no provider for the model offers it.

## HTTP status

`400 invalid_request_error`

## Typical cause

Your conversation history contains round-tripped Response API output items (for example `custom_tool_call` items or `refusal` content parts), and no provider for the model serves the Response API natively.

## Resolution

Use a model with native Response API support.