Claude API in Go

Call the Claude API from Go using the official Anthropic Go SDK. Install the package, create a client, and send your first message with full type safety.

The official Anthropic Go SDK provides full type safety and supports all Claude API features.

Installation

go get github.com/anthropics/anthropic-sdk-go

Basic message

package main

import (
    "context"
    "fmt"
    "os"

    anthropic "github.com/anthropics/anthropic-sdk-go"
    "github.com/anthropics/anthropic-sdk-go/option"
)

func main() {
    client := anthropic.NewClient(
        option.WithAPIKey(os.Getenv("ANTHROPIC_API_KEY")),
    )

    message, err := client.Messages.New(
        context.Background(),
        anthropic.MessageNewParams{
            Model:     anthropic.F(anthropic.ModelClaudeSonnet4_6),
            MaxTokens: anthropic.F(int64(1024)),
            Messages: anthropic.F([]anthropic.MessageParam{
                anthropic.UserMessage("What is the capital of France?"),
            }),
        },
    )
    if err != nil {
        fmt.Fprintf(os.Stderr, "Error: %v
", err)
        os.Exit(1)
    }

    fmt.Println(message.Content[0].(anthropic.TextBlock).Text)
}

With system prompt

message, err := client.Messages.New(
    context.Background(),
    anthropic.MessageNewParams{
        Model:     anthropic.F(anthropic.ModelClaudeSonnet4_6),
        MaxTokens: anthropic.F(int64(1024)),
        System: anthropic.F([]anthropic.TextBlockParam{
            {Type: anthropic.F(anthropic.TextBlockParamTypeText),
             Text: anthropic.F("You are a concise technical assistant.")},
        }),
        Messages: anthropic.F([]anthropic.MessageParam{
            anthropic.UserMessage("Explain goroutines briefly."),
        }),
    },
)

Streaming

stream := client.Messages.NewStreaming(
    context.Background(),
    anthropic.MessageNewParams{
        Model:     anthropic.F(anthropic.ModelClaudeSonnet4_6),
        MaxTokens: anthropic.F(int64(1024)),
        Messages: anthropic.F([]anthropic.MessageParam{
            anthropic.UserMessage("Write a Go function that reads a CSV file."),
        }),
    },
)

for stream.Next() {
    event := stream.Current()
    if delta, ok := event.Delta.(anthropic.ContentBlockDeltaEventDelta); ok {
        if delta.Type == "text_delta" {
            fmt.Print(delta.Text)
        }
    }
}
if err := stream.Err(); err != nil {
    fmt.Fprintf(os.Stderr, "Stream error: %v
", err)
}

See the Python quickstart or Node.js quickstart for equivalents in other languages. For cost estimates on Go workloads, use the Claude API Cost Calculator.

Frequently asked questions

Free tools

More examples