> ## 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.

# Reasoning Models

> Production-revalidated guidance for using Crazyrouter reasoning features and choosing the right protocol

> Last updated: 2026-06-06

# Reasoning Models

This page only documents reasoning behavior that was revalidated against Crazyrouter production on `2026-03-22`.

For OpenAI-compatible integrations, the current guidance is:

* If you only want stronger reasoning and only need the final answer, use Chat Completions with `reasoning_effort`
* If you need a stable, inspectable reasoning output, prefer the Responses API and see [GPT-5 Thinking Mode](/en/chat/responses/gpt5-thinking)

## Verified combinations

| Route            | Model     | Request parameter                        | Current production behavior                       |
| ---------------- | --------- | ---------------------------------------- | ------------------------------------------------- |
| Chat Completions | `gpt-5.5` | `reasoning_effort`                       | Request succeeds and returns a final answer       |
| Responses        | `gpt-5.5` | `reasoning.effort` / `reasoning.summary` | `output` includes `reasoning` and `message` items |

***

## Chat Completions: `reasoning_effort`

The following request shape currently works in production:

```bash cURL theme={null}
curl https://api.crazyrouter.com/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "gpt-5.5",
    "messages": [
      {
        "role": "user",
        "content": "Which is larger, 9.11 or 9.9? Explain briefly."
      }
    ],
    "reasoning_effort": "high",
    "max_tokens": 120
  }'
```

Available `reasoning_effort` values:

| Value    | Meaning                           |
| -------- | --------------------------------- |
| `low`    | Faster response for simpler tasks |
| `medium` | Balanced default-style setting    |
| `high`   | More reasoning for harder tasks   |

### Current response behavior

In the `2026-03-22` production recheck:

* the request succeeded
* the final answer was returned in `message.content`
* `message.reasoning_content` did not reliably contain usable content

So if you only want stronger reasoning, Chat Completions with `reasoning_effort` is still usable. If you need a visible reasoning summary field, do not treat Chat Completions as the primary path.

***

## When you need inspectable reasoning output

The more reliable production path is the Responses API:

```bash cURL theme={null}
curl https://api.crazyrouter.com/v1/responses \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "gpt-5.5",
    "input": "Which is larger, 9.11 or 9.9? Explain briefly.",
    "reasoning": {
      "effort": "high",
      "summary": "detailed"
    }
  }'
```

Verified `output.type` values:

```json theme={null}
["reasoning", "message"]
```

For concrete response shapes, summary fields, and streaming event names, see:

* [GPT-5 Thinking Mode](/en/chat/responses/gpt5-thinking)
* [AI Thinking Fields](/en/reference/thinking)

***

## Current recommendation

* For new builds that need to log or display reasoning summaries, start with the Responses API
* For existing Chat Completions integrations that only care about the final answer, `reasoning_effort` is still a valid path
* Do not assume all OpenAI-compatible reasoning models will reliably expose `reasoning_content`

<Warning>
  Reasoning requests usually increase both latency and token usage. Higher `reasoning_effort` generally costs more.
</Warning>