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LangWatch supports tracing Anthropic Claude API calls using the same otelopenai middleware used for OpenAI. Configure the client to point to Anthropic’s API endpoint.

​
Installation

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

​
Usage

Set LANGWATCH_API_KEY and ANTHROPIC_API_KEY environment variables before running.
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 Anthropic client via OpenAI-compatible API
	client := openai.NewClient(
		oaioption.WithAPIKey(os.Getenv("ANTHROPIC_API_KEY")),
		oaioption.WithBaseURL(os.Getenv("ANTHROPIC_BASE_URL")),
		oaioption.WithMiddleware(otelopenai.Middleware("my-app",
			otelopenai.WithCaptureInput(),
			otelopenai.WithCaptureOutput(),
			otelopenai.WithGenAISystem("anthropic"),
		)),
	)

	response, err := client.Chat.Completions.New(ctx, openai.ChatCompletionNewParams{
		Model: "claude-4-5-sonnet",
		Messages: []openai.ChatCompletionMessageParamUnion{
			openai.SystemMessage("You are a helpful assistant."),
			openai.UserMessage("Hello, Claude!"),
		},
	})
	if err != nil {
		log.Fatalf("Chat completion failed: %v", err)
	}

	log.Printf("Response: %s", response.Choices[0].Message.Content)
}
The defer tp.Shutdown(ctx) call is essential. Without it, traces buffered in memory will be lost when your application exits.