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

# Responses API Overview

> Production-revalidated guidance for choosing between Responses API and Chat Completions on Crazyrouter

> Дата обновления: 2026-06-06

# Responses API Overview

The Responses API is currently one of the main routes for newer GPT capabilities on Crazyrouter.

This page only documents conclusions that were revalidated against production on `2026-03-22`.

<Note>
  In the current production-verified scope, Claude supports only `POST /v1/messages` and `POST /v1/chat/completions`, not `POST /v1/responses`. Treat the Responses pages as GPT-first guidance.
</Note>

## Current framing

* If you need inspectable reasoning output, prefer `/v1/responses`
* If you need OpenAI-style web search, prefer `/v1/responses`
* If you only need ordinary chat or want to keep an existing integration, `/v1/chat/completions` is still fine

## Responses API vs Chat Completions API

| Dimension               | Responses API                      | Chat Completions API                                                                   |
| ----------------------- | ---------------------------------- | -------------------------------------------------------------------------------------- |
| Endpoint                | `/v1/responses`                    | `/v1/chat/completions`                                                                 |
| Input shape             | `input`                            | `messages`                                                                             |
| Output shape            | `output[]` item list               | `choices[].message`                                                                    |
| GPT reasoning           | Verified `reasoning` item          | `reasoning_effort` works, but `reasoning_content` is not stable                        |
| OpenAI-style web search | Verified `web_search_preview` path | The older `web_search` shape did not produce a stable verifiable trigger in this round |
| Streaming               | Richer event types                 | Traditional delta SSE                                                                  |

***

## Smallest useful example

```python Python theme={null}
from openai import OpenAI

client = OpenAI(
    api_key="YOUR_API_KEY",
    base_url="https://api.crazyrouter.com/v1"
)

response = client.responses.create(
    model="gpt-5.5",
    input="Explain what a REST API is in one sentence."
)

print(response.output_text)
```

In the current production recheck, this kind of minimal request returned:

```json theme={null}
{
  "object": "response",
  "output": [
    {
      "type": "message"
    }
  ]
}
```

***

## When to prefer Responses

* You need `gpt-5.5` reasoning summaries
* You need to verify whether the model actually triggered `web_search_call`
* You want richer SSE events

Related pages:

* [GPT-5 Thinking Mode](/ru/chat/responses/gpt5-thinking)
* [Responses Web Search](/ru/chat/responses/web-search)
* [Responses Function Calling](/ru/chat/responses/function-calling)

***

## When to keep Chat Completions

* You already have a stable Chat Completions integration
* You only care about the final answer, not the `reasoning` item
* You are integrating Claude, Gemini, or other OpenAI-compatible models

<Note>
  Both APIs can coexist in the same project. In practice, the better pattern is usually not a full migration, but moving only the requests that need newer capabilities onto `/v1/responses`.
</Note>