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LangWatch provides seamless, automatic instrumentation for the official openai-go client library through a dedicated middleware. This approach captures detailed information about your OpenAI API calls—including requests, responses, token usage, and streaming data—without requiring manual tracing around each call.

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Basic Usage

Instrumenting your OpenAI client involves adding the otelopenai.Middleware to its configuration. The middleware will then automatically create detailed trace spans for each API call.
The following example assumes you have already configured the LangWatch SDK. See the Go setup guide for details. For complete API documentation of all middleware options, see the OpenAI Instrumentation section in the reference.
package main

import (
	"context"
	"log"
	"os"

	"github.com/langwatch/langwatch/sdk-go"
	otelopenai "github.com/langwatch/langwatch/sdk-go/instrumentation/openai"
	"github.com/openai/openai-go"
	oaioption "github.com/openai/openai-go/option"
)

func main() {
	ctx := context.Background()
	// Assumes LangWatch is already set up.

	// Create an instrumented OpenAI client
	client := openai.NewClient(
		oaioption.WithAPIKey(os.Getenv("OPENAI_API_KEY")),
		// Add the middleware
		oaioption.WithMiddleware(otelopenai.Middleware("my-llm-app",
			// Optional: Capture request/response content
			otelopenai.WithCaptureInput(),
			otelopenai.WithCaptureOutput(),
		)),
	)

	// Create a trace for your overall operation
	tracer := langwatch.Tracer("my-llm-app")
	ctx, span := tracer.Start(ctx, "UserRequestHandler")
	defer span.End()

	// Make an API call as usual. A span will be automatically created for this call.
	response, err := client.Chat.Completions.New(ctx, openai.ChatCompletionNewParams{
		Model: openai.ChatModelGPT4oMini,
		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("Chat completion: %s", response.Choices[0].Message.Content)
}

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Configuration Options

The Middleware function accepts a required instrumentationName string followed by optional configuration functions to customize its behavior.
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WithCaptureInput()
function
Records the full input payload (e.g., messages, model) as the llm.request.body span attribute.
otelopenai.Middleware("my-app", otelopenai.WithCaptureInput())
Use with caution if conversations contain sensitive data.
​
WithCaptureOutput()
function
Records the full response payload as the llm.response.body span attribute. For streams, this contains the final, accumulated response.
otelopenai.Middleware("my-app", otelopenai.WithCaptureOutput())
​
WithGenAISystem(system string)
function
Sets the gen_ai.system attribute on spans, which is useful for identifying the underlying model provider. Defaults to "openai".
// Example for an OpenAI-compatible API from Anthropic
otelopenai.Middleware("my-app", 
    otelopenai.WithGenAISystem("anthropic"),
)
​
WithTracerProvider(provider trace.TracerProvider)
function
Specifies the OpenTelemetry TracerProvider to use. Defaults to the global provider.
// Provide a custom tracer provider
otelopenai.Middleware("my-app", 
    otelopenai.WithTracerProvider(customProvider),
)

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Streaming Support

The middleware has full, built-in support for streaming responses. It automatically processes Server-Sent Events (SSE) to capture and accumulate the streamed content, recording the final result in the span’s output field. No extra configuration is needed—just use the streaming methods of the OpenAI client as you normally would. 
import (
    "fmt"
    "log"
    "strings"
    "github.com/openai/openai-go"
)
// ... inside a function with an instrumented `client` and `ctx`

// Create a streaming request
stream, err := client.Chat.Completions.NewStreaming(ctx, openai.ChatCompletionNewParams{
	Model: openai.ChatModelGPT4oMini,
	Messages: []openai.ChatCompletionMessageParamUnion{
		openai.UserMessage("Tell me a long story about a robot."),
	},
	Stream: openai.F(true),
})
if err != nil {
    log.Fatalf("Streaming request failed: %v", err)
}
defer stream.Close() // Always close the stream

// Process the stream as usual
var fullResponse strings.Builder
for stream.Next() {
	chunk := stream.Current()
	content := chunk.Choices[0].Delta.Content
	fullResponse.WriteString(content)
	fmt.Print(content)
}

if err := stream.Err(); err != nil {
	log.Fatalf("Stream error: %v", err)
}

// The complete story is automatically captured and sent to LangWatch.

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Multi-Provider Examples

You can use the same instrumentation for any OpenAI-compatible API.

​
Anthropic (Claude)

import (
	"os"
	otelopenai "github.com/langwatch/langwatch/sdk-go/instrumentation/openai"
	"github.com/openai/openai-go"
	oaioption "github.com/openai/openai-go/option"
)

client := openai.NewClient(
	oaioption.WithBaseURL("https://api.anthropic.com/v1"),
	oaioption.WithAPIKey(os.Getenv("ANTHROPIC_API_KEY")),
	oaioption.WithMiddleware(otelopenai.Middleware("my-app-anthropic",
		otelopenai.WithGenAISystem("anthropic"),
		// other options...
	)),
)

​
Azure OpenAI

import (
	"os"
	otelopenai "github.com/langwatch/langwatch/sdk-go/instrumentation/openai"
	"github.com/openai/openai-go"
	oaioption "github.com/openai/openai-go/option"
)

client := openai.NewClient(
	oaioption.WithBaseURL("https://your-resource.openai.azure.com/openai/deployments/your-deployment"),
	oaioption.WithAPIKey(os.Getenv("AZURE_OPENAI_API_KEY")),
	oaioption.WithMiddleware(otelopenai.Middleware("my-app-azure",
		otelopenai.WithGenAISystem("azure"),
		// other options...
	)),
)

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Supported Operations

The middleware traces all requests made through the instrumented client, with enriched support for specific operations:
APISupport LevelDetails
Chat CompletionsFullCaptures request/response, token usage, model info.
Chat Completions StreamingFullAccumulates streaming chunks into a final response.
EmbeddingsFullCaptures input text and embedding vector dimensions.
ImagesPartial (Input)Captures image generation prompts and parameters.
AudioPartial (Input)Captures audio generation request parameters.
“Partial” support means that while the call is traced, only the input parameters are captured, not the generated binary content (image/audio).

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Installation

go get github.com/langwatch/langwatch/sdk-go/instrumentation/openai

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Collected Attributes

The middleware adds comprehensive attributes following OpenTelemetry GenAI Semantic Conventions:

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Request Attributes

  • gen_ai.system (e.g., "openai")
  • gen_ai.request.model
  • gen_ai.request.temperature
  • gen_ai.request.top_p
  • gen_ai.request.top_k
  • gen_ai.request.frequency_penalty