> ## 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.

# Create Chat Completion

> Production-oriented usage of POST /v1/chat/completions based on current live behavior

> Last updated: 2026-06-06

# Create Chat Completion

```
POST /v1/chat/completions
```

Generates model responses from a message list and supports both non-streaming and streaming output.

This page only documents common behavior revalidated against Crazyrouter production on `2026-03-23`.

## Authentication

```text theme={null}
Authorization: Bearer YOUR_API_KEY
```

## Core parameters

| Parameter         | Type           | Required | Meaning                                                              |
| ----------------- | -------------- | -------- | -------------------------------------------------------------------- |
| `model`           | string         | Yes      | Model name such as `gpt-5.5`, `claude-opus-4-8`, or `gemini-3.1-pro` |
| `messages`        | array          | Yes      | Message list                                                         |
| `stream`          | boolean        | No       | Whether to stream output                                             |
| `max_tokens`      | integer        | No       | Maximum output tokens                                                |
| `temperature`     | number         | No       | Sampling temperature                                                 |
| `response_format` | object         | No       | Structured output constraint                                         |
| `tools`           | array          | No       | Tool list                                                            |
| `tool_choice`     | string\|object | No       | Tool-selection strategy                                              |
| `stream_options`  | object         | No       | Streaming extras such as `include_usage`                             |

<Note>
  Optional parameter support varies by model. Client code should rely on the stable common fields first rather than assuming every model supports the same advanced options.
</Note>

***

## Non-streaming request

```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": "system",
        "content": "You are a helpful assistant."
      },
      {
        "role": "user",
        "content": "Explain artificial intelligence in one sentence."
      }
    ],
    "max_tokens": 64
  }'
```

Typical production shape:

```json theme={null}
{
  "object": "chat.completion",
  "model": "gpt-5.5",
  "choices": [
    {
      "message": {
        "role": "assistant",
        "content": "...",
        "reasoning_content": null,
        "tool_calls": null
      },
      "finish_reason": "stop"
    }
  ]
}
```

### Important interpretation

* `message.content` is the most stable final-text field
* `message.tool_calls` only appears when the model is requesting tool execution
* `message.reasoning_content` may exist as a key, but should not currently be treated as guaranteed usable content

***

## Streaming request

```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": "Explain AI in one short sentence."
      }
    ],
    "stream": true,
    "stream_options": {
      "include_usage": true
    },
    "max_tokens": 64
  }'
```

This production recheck confirmed that:

* streaming returns `chat.completion.chunk`
* SSE chunks are sent as `data: ...`
* the stream still ends with `data: [DONE]`

Observed SSE shape:

```text theme={null}
data: {"object":"chat.completion.chunk","model":"gpt-5.5","choices":[{"delta":{"role":"assistant","content":"AI","reasoning_content":null,"tool_calls":null}}]}
```

```text theme={null}
data: [DONE]
```

***

## Python example

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

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

stream = client.chat.completions.create(
    model="gpt-5.5",
    messages=[
        {"role": "user", "content": "Explain AI in one short sentence."}
    ],
    stream=True,
    stream_options={"include_usage": True},
    max_tokens=64
)

for chunk in stream:
    delta = chunk.choices[0].delta
    if delta.content is not None:
        print(delta.content, end="")
```

***

## Current recommendation

* For normal text chat, use `/v1/chat/completions`
* For reasoning summaries or OpenAI-style web search, prefer `/v1/responses`
* For more specific capability guarantees, use the dedicated capability pages rather than this generic endpoint page

Related pages:

* [Chat Completion Object](/en/chat/openai/overview)
* [Reasoning Models](/en/chat/openai/reasoning)
* [Web Search](/en/chat/openai/web-search)