> ## 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.

# OpenRouter Integration

> Instrument OpenRouter model calls in Go with LangWatch to compare models, track quality, and run AI agent evaluations.

[OpenRouter](https://openrouter.ai) provides a unified API to access a vast range of LLMs from different providers. LangWatch can trace calls made through OpenRouter using its OpenAI-compatible endpoint.

## Setup

You will need an OpenRouter API key from your [OpenRouter settings](https://openrouter.ai/keys).

Set your OpenRouter API key as an environment variable:

```bash  theme={null}
export OPENROUTER_API_KEY="your-openrouter-api-key"
```

## Usage

<Info>
  Set `LANGWATCH_API_KEY` and `OPENROUTER_API_KEY` environment variables before running.
</Info>

The key difference with OpenRouter is the model name, which is prefixed with the provider (e.g., `anthropic/claude-sonnet-4-20250514`).

```go  theme={null}
package main

import (
	"context"
	"log"
	"os"

	langwatch "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"
	"go.opentelemetry.io/otel"
	sdktrace "go.opentelemetry.io/otel/sdk/trace"
)

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

	// Set up LangWatch exporter
	exporter, err := langwatch.NewDefaultExporter(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 OpenRouter client via OpenAI-compatible API
	client := openai.NewClient(
		oaioption.WithBaseURL("https://openrouter.ai/api/v1"),
		oaioption.WithAPIKey(os.Getenv("OPENROUTER_API_KEY")),
		oaioption.WithMiddleware(otelopenai.Middleware("my-app",
			otelopenai.WithCaptureInput(),
			otelopenai.WithCaptureOutput(),
			otelopenai.WithGenAISystem("openrouter"),
		)),
	)

	response, err := client.Chat.Completions.New(ctx, openai.ChatCompletionNewParams{
		Model: "anthropic/claude-3.5-sonnet",
		Messages: []openai.ChatCompletionMessageParamUnion{
			openai.UserMessage("Hello via OpenRouter!"),
		},
	})
	if err != nil {
		log.Fatalf("OpenRouter API call failed: %v", err)
	}

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

<Warning>
  The `defer tp.Shutdown(ctx)` call is essential. Without it, traces buffered in memory will be lost when your application exits.
</Warning>

<Note>
  Using OpenRouter is a great way to experiment with different models without changing your core instrumentation logic. All calls will be traced by LangWatch, regardless of the underlying model you choose.
</Note>