OpenRouter 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.

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Setup

You will need an OpenRouter API key from your OpenRouter settings. Set your OpenRouter API key as an environment variable: 
export OPENROUTER_API_KEY="your-openrouter-api-key"

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Example

Configure your openai.Client to use the OpenRouter base URL and your API key. Set the gen_ai.system attribute to "openrouter" for clear identification in your LangWatch traces. The key difference with OpenRouter is the model name, which is typically prefixed with the original provider (e.g., anthropic/claude-3.5-sonnet).
The following example assumes you have already configured the LangWatch SDK. See the Go setup guide for details.
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.

	client := openai.NewClient(
		// Use the OpenRouter API endpoint
		oaioption.WithBaseURL("https://openrouter.ai/api/v1"),

		// Use your OpenRouter API key
		oaioption.WithAPIKey(os.Getenv("OPENROUTER_API_KEY")),

		// Add the middleware, identifying the system as "openrouter"
		oaioption.WithMiddleware(otelopenai.Middleware("my-openrouter-app",
			otelopenai.WithGenAISystem("openrouter"),
			otelopenai.WithCaptureInput(),
			otelopenai.WithCaptureOutput(),
		)),
	)

	// Make a call to a model available on OpenRouter
	response, err := client.Chat.Completions.New(ctx, openai.ChatCompletionNewParams{
		// Model names are prefixed with the provider
		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 from OpenRouter: %s", response.Choices[0].Message.Content)
}
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.