Welcome to the Anthropic Go SDK

Relevant source files

The following files were used as context for generating this wiki page:

• README.md
• CONTRIBUTING.md
• examples/message/main.go
• examples/message-streaming/main.go
• examples/tools/main.go
• vertex/vertex.go (referenced via examples/vertex/main.go)
• bedrock/bedrock.go (referenced via examples/bedrock/main.go)
• schemautil.go

The Anthropic Go SDK provides a robust, type-safe interface for Go applications to interact with the Anthropic Claude API. It supports a wide array of features including text generation, message streaming, multimodal inputs (images and documents), and tool use (function calling). The SDK is designed to be extensible, offering specialized support for cloud providers like Google Vertex AI and AWS Bedrock.

Most of the SDK code is automatically generated, ensuring consistency with the official OpenAPI specification, while the lib/ and examples/ directories are reserved for manual modifications and implementation guides.
Sources: README.md:7-9, CONTRIBUTING.md:16-19

Core Architecture and Initialization

The SDK revolves around a central Client object created via anthropic.NewClient(). Configuration is handled through functional options, allowing users to specify API keys, base URLs, and cloud-specific authentication.

The diagram above illustrates the initialization flow and the service hierarchy within the client.
Sources: README.md:31-35, examples/file-upload/main.go:16-17, betamessagebatch_test.go:28-31

Authentication Methods

Method	Provider	Description
option.WithAPIKey	Anthropic	Sets the standard ANTHROPIC_API_KEY. Defaults to environment lookup.
vertex.WithGoogleAuth	Google Cloud	Configures OAuth for Vertex AI with Region and Project ID.
bedrock.WithLoadDefaultConfig	AWS	Loads AWS credentials from environment (e.g., AWS_BEARER_TOKEN_BEDROCK).
Sources: README.md:32, examples/vertex/main.go:14-16, examples/bedrock-bearer-token/main.go:26-28

Message Interaction

The primary interface for generating text is the Messages service. It provides two main modes: synchronous requests and streaming responses.

Synchronous Messages

Synchronous calls block until the full response is received. Developers define MessageNewParams containing the model, max tokens, and an array of Messages.

message, err := client.Messages.New(ctx, anthropic.MessageNewParams{
    MaxTokens: 1024,
    Messages:  []anthropic.MessageParam{anthropic.NewUserMessage(anthropic.NewTextBlock("Query"))},
    Model:     anthropic.ModelClaudeSonnet4_5_20250929,
})

Sources: examples/message/main.go:15-22, usage_test.go:31-41

Streaming Messages

Streaming allows applications to process responses incrementally. The NewStreaming method returns a Stream object that can be iterated over using .Next() and .Current().

The sequence diagram shows the flow of Server-Sent Events from the API to the application layer.
Sources: examples/message-streaming/main.go:19-24, examples/message-streaming/main.go:28-40

Advanced Features

Tool Use (Function Calling)

The SDK enables Claude to interact with external functions. Tools are defined with a Name, Description, and a JSON Schema for inputs. The SDK includes a schemautil.go utility to transform standard JSON schemas into the specific format required by the Anthropic API (e.g., forcing additionalProperties: false).
Sources: examples/tools/main.go:26-40, schemautil.go:78-100

Multimodal Support

Claude can process images and documents alongside text.

• Images: Encoded as Base64 strings within NewImageBlockBase64.
• Documents: Uploaded via the Beta.Files service and referenced by ID in NewBetaDocumentBlock.
  Sources: examples/multimodal/main.go:23-42, examples/file-upload/main.go:23-46

Beta Features and Schema Utilities

The Beta service namespace contains experimental features such as:

• Structured Outputs: Forcing model responses into a specific JSON schema using OutputFormat.
• Message Batches: Submitting multiple requests for asynchronous processing.
• Context Management: Features like CacheControl to optimize token usage.
  Sources: examples/structured-outputs/main.go:42-45, betamessage_test.go:41-47, betamessagebatch_test.go:32-35

Development and Testing

The repository includes a robust suite of scripts for local development.

Command	Purpose
./scripts/bootstrap	Installs dependencies and builds the SDK.
./scripts/lint	Runs code linters.
./scripts/mock	Starts a mock server based on the OpenAPI spec for testing.
./scripts/test	Executes the test suite.
go run ./examples/<name>	Runs a specific implementation example.
Sources: CONTRIBUTING.md:10-12, CONTRIBUTING.md:27-29, CONTRIBUTING.md:46-52

Summary

The Anthropic Go SDK is a comprehensive toolset for integrating Claude into Go environments. It balances ease of use with powerful low-level control, providing type safety for complex features like Tool Use and Beta API access. By supporting multiple cloud providers and offering utilities for schema transformation, it serves as a flexible foundation for building AI-native applications.