go changed

The first capture of this source. The page was already there, and this is what it said.

---
title: Go SDK
url: https://platform.claude.com/docs/en/cli-sdks-libraries/sdks/go
description: Install and configure the Anthropic Go SDK with context-based cancellation and functional options
---

The Anthropic Go library provides convenient access to the Claude API from applications written in Go.

<Info>
  For API feature documentation with code examples, see the [API reference](https://platform.claude.com/docs/en/api/overview). This page covers Go-specific SDK features and configuration.
</Info>

## Installation

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

Install with `go get`:

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

## Requirements

This library requires Go 1.23+.

## Usage

```go
package main

import (
	"context"
	"fmt"

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

func main() {
	client := anthropic.NewClient(
		option.WithAPIKey("my-anthropic-api-key"), // defaults to os.LookupEnv("ANTHROPIC_API_KEY")
	)
	message, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
		MaxTokens: 1024,
		Messages: []anthropic.MessageParam{
			anthropic.NewUserMessage(anthropic.NewTextBlock("What is a quaternion?")),
		},
		Model: anthropic.ModelClaudeOpus5,
	})
	if err != nil {
		panic(err.Error())
	}
	for _, block := range message.Content {
		if textBlock, ok := block.AsAny().(anthropic.TextBlock); ok {
			fmt.Println(textBlock.Text)
		}
	}
}
```

For authentication options including Workload Identity Federation, see [Authentication](https://platform.claude.com/docs/en/manage-claude/authentication).

<AccordionGroup>
  <Accordion title="Conversations">
    ```go
    messages := []anthropic.MessageParam{
    	anthropic.NewUserMessage(anthropic.NewTextBlock("What is my first name?")),
    }

    message, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
    	Model:     anthropic.ModelClaudeOpus5,
    	Messages:  messages,
    	MaxTokens: 1024,
    })
    if err != nil {
    	panic(err)
    }

    fmt.Printf("%+v\n", message.Content)

    messages = append(messages, message.ToParam())
    messages = append(messages, anthropic.NewUserMessage(
    	anthropic.NewTextBlock("My full name is John Doe"),
    ))

    message, err = client.Messages.New(context.TODO(), anthropic.MessageNewParams{
    	Model:     anthropic.ModelClaudeOpus5,
    	Messages:  messages,
    	MaxTokens: 1024,
    })
    if err != nil {
    	panic(err)
    }

    fmt.Printf("%+v\n", message.Content)
    ```
  </Accordion>

  <Accordion title="System prompts">
    ```go
    message, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
    	Model:     anthropic.ModelClaudeOpus5,
    	MaxTokens: 1024,
    	System: []anthropic.TextBlockParam{
    		{Text: "Be very serious at all times."},
    	},
    	Messages: messages,
    })
    if err != nil {
    	panic(err)
    }
    fmt.Printf("%+v\n", message.Content)
    ```
  </Accordion>

  <Accordion title="Streaming">
    ```go
    content := "What is a quaternion?"

    stream := client.Messages.NewStreaming(context.TODO(), anthropic.MessageNewParams{
    	Model:     anthropic.ModelClaudeOpus5,
    	MaxTokens: 1024,
    	Messages: []anthropic.MessageParam{
    		anthropic.NewUserMessage(anthropic.NewTextBlock(content)),
    	},
    })

    message := anthropic.Message{}
    for stream.Next() {
    	event := stream.Current()
    	err := message.Accumulate(event)
    	if err != nil {
    		panic(err)
    	}

    	switch eventVariant := event.AsAny().(type) {
    	case anthropic.ContentBlockDeltaEvent:
    		switch deltaVariant := eventVariant.Delta.AsAny().(type) {
    		case anthropic.TextDelta:
    			print(deltaVariant.Text)
    		}

    	}
    }

    if stream.Err() != nil {
    	panic(stream.Err())
    }
    ```
  </Accordion>

  <Accordion title="Tool calling">
    ```go
    messages := []anthropic.MessageParam{
    	anthropic.NewUserMessage(anthropic.NewTextBlock(content)),
    }

    toolParams := []anthropic.ToolParam{
    	{
    		Name:        "get_coordinates",
    		Description: anthropic.String("Accepts a place as an address, then returns the latitude and longitude coordinates."),
    		InputSchema: GetCoordinatesInputSchema,
    	},
    }
    tools := make([]anthropic.ToolUnionParam, len(toolParams))
    for i, toolParam := range toolParams {
    	tools[i] = anthropic.ToolUnionParam{OfTool: &toolParam}
    }

    for {
    	message, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
    		Model:     anthropic.ModelClaudeOpus5,
    		MaxTokens: 1024,
    		Messages:  messages,
    		Tools:     tools,
    	})

    	if err != nil {
    		panic(err)
    	}

    	print(color("[assistant]: "))
    	for _, block := range message.Content {
    		switch block := block.AsAny().(type) {
    		case anthropic.TextBlock:
    			println(block.Text)
    			println()
    		case anthropic.ToolUseBlock:
    			inputJSON, _ := json.Marshal(block.Input)
    			println(block.Name + ": " + string(inputJSON))
    			println()
    		}
    	}

    	messages = append(messages, message.ToParam())
    	toolResults := []anthropic.ContentBlockParamUnion{}

    	for _, block := range message.Content {
    		switch variant := block.AsAny().(type) {
    		case anthropic.ToolUseBlock:
    			print(color("[user (" + block.Name + ")]: "))

    			var response interface{}
    			switch block.Name {
    			case "get_coordinates":
    				var input struct {
    					Location string `json:"location"`
    				}

    				err := json.Unmarshal([]byte(variant.JSON.Input.Raw()), &input)
    				if err != nil {
    					panic(err)
    				}

    				response = GetCoordinates(input.Location)
    			}

    			b, err := json.Marshal(response)
    			if err != nil {
    				panic(err)
    			}

    			println(string(b))

    			toolResults = append(toolResults, anthropic.NewToolResultBlock(block.ID, string(b), false))
    		}

    	}
    	if len(toolResults) == 0 {
    		break
    	}
    	messages = append(messages, anthropic.NewUserMessage(toolResults...))
    }
    ```
  </Accordion>
</AccordionGroup>

## Request fields

The anthropic library uses the [`omitzero`](https://tip.golang.org/doc/go1.24#encodingjsonpkgencodingjson) semantics from the Go 1.24+ `encoding/json` release for request fields.

Required primitive fields (such as `int64` or `string`) feature the tag `` `json:"...,required"` ``. These fields are always serialized, even their zero values.

Optional primitive types are wrapped in a `param.Opt[T]`. These fields can be set with the provided constructors, such as `anthropic.String(string)` or `anthropic.Int(int64)`.

Any `param.Opt[T]`, map, slice, struct or string enum uses the tag `` `json:"...,omitzero"` ``. Its zero value is considered omitted.

The `param.IsOmitted(any)` function can confirm the presence of any `omitzero` field.

```go
p := anthropic.ExampleParams{
	ID:   "id_xxx",                // required property
	Name: anthropic.String("..."), // optional property

	Point: anthropic.Point{
		X: 0,                // required field will serialize as 0
		Y: anthropic.Int(1), // optional field will serialize as 1
		// ... omitted non-required fields will not be serialized
	},

	Origin: anthropic.Origin{}, // the zero value of [Origin] is considered omitted
}
```

To send `null` instead of a `param.Opt[T]`, use `param.Null[T]()`. To send `null` instead of a struct `T`, use `param.NullStruct[T]()`.

```go
p.Name = param.Null[string]()       // 'null' instead of string
p.Point = param.NullStruct[Point]() // 'null' instead of struct

param.IsNull(p.Name)  // true
param.IsNull(p.Point) // true
```

Request structs contain a `.SetExtraFields(map[string]any)` method which can send non-conforming fields in the request body. Extra fields overwrite any struct fields with a matching key.

<Warning>
  For security reasons, only use `SetExtraFields` with trusted data.
</Warning>

To send a custom value instead of a struct, use the generic function `param.Override` (for example, `param.Override[anthropic.FooParams](12)`).

```go
// In cases where the API specifies a given type,
// but you want to send something else, use [SetExtraFields]:
p.SetExtraFields(map[string]any{
	"x": 0.01, // send "x" as a float instead of int
})

// Send a number instead of an object
custom := param.Override[anthropic.FooParams](12)
```

### Request unions

Cut at 300 lines. The page has the rest.