> ## Documentation Index
> Fetch the complete documentation index at: https://openrouter-d02e98a0-mintlify-5b6e02fd.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# ChatStreamChunk - Go SDK

> ChatStreamChunk type definition

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

Streaming chat completion chunk

## Fields

| Field                | Type                                                                                           | Required             | Description                                                     | Example                                                                                                                                                                                                                                                                                                                                                                                             |
| -------------------- | ---------------------------------------------------------------------------------------------- | -------------------- | --------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `Choices`            | \[][components.ChatStreamChoice](/client-sdks/go/api-reference/models/chatstreamchoice)        | :heavy\_check\_mark: | List of streaming chunk choices                                 |                                                                                                                                                                                                                                                                                                                                                                                                     |
| `Created`            | `int64`                                                                                        | :heavy\_check\_mark: | Unix timestamp of creation                                      | 1677652288                                                                                                                                                                                                                                                                                                                                                                                          |
| `Error`              | [\*components.Error](/client-sdks/go/api-reference/models/error)                               | :heavy\_minus\_sign: | Error information                                               | `{"code": 429,"message": "Rate limit exceeded"}`                                                                                                                                                                                                                                                                                                                                                    |
| `ID`                 | `string`                                                                                       | :heavy\_check\_mark: | Unique chunk identifier                                         | chatcmpl-123                                                                                                                                                                                                                                                                                                                                                                                        |
| `Model`              | `string`                                                                                       | :heavy\_check\_mark: | Model used for completion                                       | openai/gpt-4                                                                                                                                                                                                                                                                                                                                                                                        |
| `Object`             | [components.ChatStreamChunkObject](/client-sdks/go/api-reference/models/chatstreamchunkobject) | :heavy\_check\_mark: | N/A                                                             |                                                                                                                                                                                                                                                                                                                                                                                                     |
| `OpenrouterMetadata` | [\*components.OpenRouterMetadata](/client-sdks/go/api-reference/models/openroutermetadata)     | :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 />}                                                                                     |
| `ServiceTier`        | optionalnullable.OptionalNullable\[`string`]                                                   | :heavy\_minus\_sign: | The service tier used by the upstream provider for this request | default                                                                                                                                                                                                                                                                                                                                                                                             |
| `SystemFingerprint`  | `*string`                                                                                      | :heavy\_minus\_sign: | System fingerprint                                              | fp\_44709d6fcb                                                                                                                                                                                                                                                                                                                                                                                      |
| `Usage`              | [\*components.ChatUsage](/client-sdks/go/api-reference/models/chatusage)                       | :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/>`} |