Claude API — Go

Note: The Go SDK supports the Claude API and beta tool use with `BetaToolRunner`. Agent SDK is not yet available for Go.

Installation

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

Client Initialization

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

// Default (uses ANTHROPIC_API_KEY env var) client := anthropic.NewClient()

// Explicit API key client := anthropic.NewClient( option.WithAPIKey("your-api-key"), ) ```

Basic Message Request

```go response, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{ Model: anthropic.ModelClaudeOpus4_6, MaxTokens: 1024, Messages: []anthropic.MessageParam{ anthropic.NewUserMessage(anthropic.NewTextBlock("What is the capital of France?")), }, }) if err != nil { log.Fatal(err) } fmt.Println(response.Content[0].Text) ```

Streaming

```go stream := client.Messages.NewStreaming(context.TODO(), anthropic.MessageNewParams{ Model: anthropic.ModelClaudeOpus4_6, MaxTokens: 1024, Messages: []anthropic.MessageParam{ anthropic.NewUserMessage(anthropic.NewTextBlock("Write a haiku")), }, })

for stream.Next() { event := stream.Current() switch eventVariant := event.AsAny().(type) { case anthropic.ContentBlockDeltaEvent: switch deltaVariant := eventVariant.Delta.AsAny().(type) { case anthropic.TextDelta: fmt.Print(deltaVariant.Text) } } } if err := stream.Err(); err != nil { log.Fatal(err) } ```

Tool Use

Tool Runner (Beta — Recommended)

Beta: The Go SDK provides `BetaToolRunner` for automatic tool use loops via the `toolrunner` package.

```go import ( "context" "fmt" "log"

"github.com/anthropics/anthropic-sdk-go"
"github.com/anthropics/anthropic-sdk-go/toolrunner"

)

// Define tool input with jsonschema tags for automatic schema generation type GetWeatherInput struct { City string `json:"city" jsonschema:"required,description=The city name"` }

// Create a tool with automatic schema generation from struct tags weatherTool, err := toolrunner.NewBetaToolFromJSONSchema( "get_weather", "Get current weather for a city", func(ctx context.Context, input GetWeatherInput) (anthropic.BetaToolResultBlockParamContentUnion, error) { return anthropic.BetaToolResultBlockParamContentUnion{ OfText: &anthropic.BetaTextBlockParam{ Text: fmt.Sprintf("The weather in %s is sunny, 72°F", input.City), }, }, nil }, ) if err != nil { log.Fatal(err) }

// Create a tool runner that handles the conversation loop automatically runner := client.Beta.Messages.NewToolRunner( []anthropic.BetaTool{weatherTool}, anthropic.BetaToolRunnerParams{ BetaMessageNewParams: anthropic.BetaMessageNewParams{ Model: anthropic.ModelClaudeOpus4_6, MaxTokens: 1024, Messages: []anthropic.BetaMessageParam{ anthropic.NewBetaUserMessage(anthropic.NewBetaTextBlock("What's the weather in Paris?")), }, }, MaxIterations: 5, }, )

// Run until Claude produces a final response message, err := runner.RunToCompletion(context.Background()) if err != nil { log.Fatal(err) } fmt.Println(message.Content[0].Text) ```

Key features of the Go tool runner:

Automatic schema generation from Go structs via `jsonschema` tags
`RunToCompletion()` for simple one-shot usage
`All()` iterator for processing each message in the conversation
`NextMessage()` for step-by-step iteration
Streaming variant via `NewToolRunnerStreaming()` with `AllStreaming()`

Manual Loop

For fine-grained control, use raw tool definitions via JSON schema. See the shared tool use concepts for the tool definition format and agentic loop pattern.

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