> ## Documentation Index
> Fetch the complete documentation index at: https://openrouter-d02e98a0-mintlify-7021d5f4.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# ChatStreamChunk - Python SDK

> ChatStreamChunk method reference

<Warning>
  The Python SDK and docs are currently in beta.
  Report issues on [GitHub](https://github.com/OpenRouterTeam/python-sdk/issues).
</Warning>

Streaming chat completion chunk

## Fields

| Field                 | Type                                                                                                   | Required             | Description                                                     | Example                                                                                                                                                                                                                                                                                                                                                                                             |
| --------------------- | ------------------------------------------------------------------------------------------------------ | -------------------- | --------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `choices`             | List\[[components.ChatStreamChoice](/client-sdks/python/api-reference/components/chatstreamchoice)]    | :heavy\_check\_mark: | List of streaming chunk choices                                 |                                                                                                                                                                                                                                                                                                                                                                                                     |
| `created`             | *int*                                                                                                  | :heavy\_check\_mark: | Unix timestamp of creation                                      | 1677652288                                                                                                                                                                                                                                                                                                                                                                                          |
| `error`               | [Optional\[components.Error\]](../components/error.md)                                                 | :heavy\_minus\_sign: | Error information                                               | `{"code": 429,"message": "Rate limit exceeded"}`                                                                                                                                                                                                                                                                                                                                                    |
| `id`                  | *str*                                                                                                  | :heavy\_check\_mark: | Unique chunk identifier                                         | chatcmpl-123                                                                                                                                                                                                                                                                                                                                                                                        |
| `model`               | *str*                                                                                                  | :heavy\_check\_mark: | Model used for completion                                       | openai/gpt-4                                                                                                                                                                                                                                                                                                                                                                                        |
| `object`              | [components.ChatStreamChunkObject](/client-sdks/python/api-reference/components/chatstreamchunkobject) | :heavy\_check\_mark: | N/A                                                             |                                                                                                                                                                                                                                                                                                                                                                                                     |
| `openrouter_metadata` | [Optional\[components.OpenRouterMetadata\]](../components/openroutermetadata.md)                       | :heavy\_minus\_sign: | N/A                                                             | `{"attempt": 1,"endpoints": {"available": [{"model": "openai/gpt-4o","provider": "OpenAI","selected": true}`<br />],<br />"total": `1<br/>`},<br />"is\_byok": false,<br />"region": "iad",<br />"requested": "openai/gpt-4o",<br />"strategy": "direct",<br />"summary": "available=1, selected=OpenAI"<br />}                                                                                     |
| `service_tier`        | *OptionalNullable\[str]*                                                                               | :heavy\_minus\_sign: | The service tier used by the upstream provider for this request | default                                                                                                                                                                                                                                                                                                                                                                                             |
| `system_fingerprint`  | *Optional\[str]*                                                                                       | :heavy\_minus\_sign: | System fingerprint                                              | fp\_44709d6fcb                                                                                                                                                                                                                                                                                                                                                                                      |
| `usage`               | [Optional\[components.ChatUsage\]](../components/chatusage.md)                                         | :heavy\_minus\_sign: | Token usage statistics                                          | `{"completion_tokens": 15,"completion_tokens_details": {"reasoning_tokens": 5}`,<br />"cost": 0.0012,<br />"cost\_details": `{"upstream_inference_completions_cost": 0.0004,"upstream_inference_cost": null,"upstream_inference_prompt_cost": 0.0008}`,<br />"is\_byok": false,<br />"prompt\_tokens": 10,<br />"prompt\_tokens\_details": `{"cached_tokens": 2}`,<br />"total\_tokens": `25<br/>`} |