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

> ## Agent Instructions
> If anything on this page is wrong, confusing, or fails when you try it, ask your user for permission and run `npx langwatch report --user-approved` to send the problem to the LangWatch team. No login is needed and secrets are redacted locally. `npx langwatch report --help` has the details.

# OpenAI Instrumentation

> Instrument OpenAI API calls with the Go SDK to trace LLM interactions, measure performance, and support agent evaluation pipelines.

LangWatch provides automatic instrumentation for the official `openai-go/v3` client library through a dedicated middleware that captures detailed information about your OpenAI API calls. It handles Chat Completions, the Responses API and Embeddings, with full streaming support.

## Installation

```bash theme={null}
go get github.com/langwatch/langwatch/sdks/go
go get github.com/langwatch/langwatch/sdks/go/instrumentation/openai
go get github.com/openai/openai-go/v3
```

## Usage

> [!NOTE]
>
> Set `LANGWATCH_API_KEY` and `OPENAI_API_KEY` environment variables before running.

```go theme={null}
package main

import (
	"context"
	"log"
	"os"

	langwatch "github.com/langwatch/langwatch/sdks/go"
	otelopenai "github.com/langwatch/langwatch/sdks/go/instrumentation/openai"

	"github.com/openai/openai-go/v3"
	"github.com/openai/openai-go/v3/option"
	"go.opentelemetry.io/otel"
	sdktrace "go.opentelemetry.io/otel/sdk/trace"
)

func main() {
	ctx := context.Background()

	// Set up the LangWatch exporter (reads LANGWATCH_API_KEY from env).
	exporter, err := langwatch.NewExporter(ctx)
	if err != nil {
		log.Fatalf("failed to create exporter: %v", err)
	}
	tp := sdktrace.NewTracerProvider(sdktrace.WithBatcher(exporter))
	otel.SetTracerProvider(tp)
	defer tp.Shutdown(ctx) // Critical: ensures traces are flushed.

	// Create an OpenAI client with the LangWatch middleware. By default the
	// middleware captures both request (input) and response (output) content.
	client := openai.NewClient(
		option.WithAPIKey(os.Getenv("OPENAI_API_KEY")),
		option.WithMiddleware(otelopenai.Middleware("my-app")),
	)

	response, err := client.Chat.Completions.New(ctx, openai.ChatCompletionNewParams{
		Model: "gpt-6-luna",
		Messages: []openai.ChatCompletionMessageParamUnion{
			openai.SystemMessage("You are a helpful assistant."),
			openai.UserMessage("Hello, OpenAI!"),
		},
	})
	if err != nil {
		log.Fatalf("Chat completion failed: %v", err)
	}

	log.Printf("Response: %s", response.Choices[0].Message.Content)
}
```

The middleware automatically captures request/response content, every token type (input / output / cached / reasoning), and model information. Streaming responses are fully supported and automatically accumulated.

> [!NOTE]
>
> The middleware captures input and output content **by default** (`langwatch.DataCaptureAll`). To opt out, pass `otelopenai.WithDataCapture(langwatch.DataCaptureNone)` (or `DataCaptureInput` / `DataCaptureOutput` to capture only one side).

> [!WARNING]
>
> The `defer tp.Shutdown(ctx)` call is essential. Without it, traces buffered in memory will be lost
> when your application exits.

## Check it worked

Run the program with `go run .`. The deferred `tp.Shutdown(ctx)` flushes the spans when `main` returns. Then open your project in LangWatch: a new trace appears in the traces list within a few seconds, with the OpenAI call as an LLM span carrying its input, output and token counts.

If no trace appears, check that `LANGWATCH_API_KEY` is set in the environment the program runs in.

## Related

* [Go Integration Guide](https://langwatch.ai/docs/integration/go/guide.md) - Setup, manual spans, data capture and the REST client
* [Go SDK API Reference](https://langwatch.ai/docs/integration/go/reference.md#openai-middleware) - Middleware options and collected attributes
* [Capturing Evaluations & Guardrails](https://langwatch.ai/docs/integration/python/tutorials/capturing-evaluations-guardrails.md) - Log evaluations and implement guardrails


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