Claude Go SDK — Quickstart

How to call the Claude API from Go in 2026. Covers the official SDK, streaming, prompt caching, tool use, and concurrency patterns for production Go services.

Anthropic ships an official Go SDK — github.com/anthropics/anthropic-sdk-go. It tracks the Python and TypeScript SDKs in feature parity (messages, streaming, batch, prompt caching, tool use, vision). This page is a working quickstart plus the Go-idiomatic patterns for production services.

Install

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

Minimum-correct call

package main

import (
    "context"
    "fmt"
    "log"

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

func main() {
    client := anthropic.NewClient(
        option.WithAPIKey("sk-ant-..."),
    )
    msg, 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.NewUserMessage(anthropic.NewTextBlock("Explain Go interfaces in 3 bullets.")),
        }),
    })
    if err != nil {
        log.Fatal(err)
    }
    for _, block := range msg.Content {
        if t, ok := block.AsAny().(anthropic.TextBlock); ok {
            fmt.Println(t.Text)
        }
    }
}

Streaming

stream := client.Messages.NewStreaming(ctx, anthropic.MessageNewParams{
    Model:     anthropic.F(anthropic.ModelClaudeSonnet4_6),
    MaxTokens: anthropic.F(int64(1024)),
    Messages:  anthropic.F([]anthropic.MessageParam{anthropic.NewUserMessage(anthropic.NewTextBlock("Write a haiku."))}),
})
for stream.Next() {
    event := stream.Current()
    if delta, ok := event.Delta.AsAny().(anthropic.RawContentBlockDeltaEventTextDelta); ok {
        fmt.Print(delta.Text)
    }
}
if err := stream.Err(); err != nil {
    log.Fatal(err)
}

Prompt caching

Cache a long system prompt by setting CacheControl on the prefix block:

system := []anthropic.TextBlockParam{{
    Type: anthropic.F(anthropic.TextBlockParamTypeText),
    Text: anthropic.F(longSystemPrompt),
    CacheControl: anthropic.F(anthropic.CacheControlEphemeralParam{
        Type: anthropic.F(anthropic.CacheControlEphemeralTypeEphemeral),
    }),
}}

Cached reads cost 10% of input price after the first request — see the caching deep-dive.

Concurrency patterns

• One client, many goroutines. The SDK client is safe for concurrent use. Share a single *Client across your service.
• Bound goroutines with a semaphore. Use golang.org/x/sync/semaphore sized to your tier's TPM divided by average tokens-per-call so you do not stampede a 429.
• Context-driven timeouts. Always pass a context.WithTimeout; the SDK respects it for both streaming and non-streaming calls.

Retries and rate limits

The Go SDK retries 429s and 5xx with exponential backoff out of the box. Configure with option.WithMaxRetries(int). For application-layer logic on 429, see 429 handling.

Tool use (function calling)

tools := []anthropic.ToolUnionParam{
    anthropic.F[anthropic.ToolUnionParam](anthropic.ToolParam{
        Name:        anthropic.F("get_weather"),
        Description: anthropic.F("Get current weather for a location."),
        InputSchema: anthropic.F(anthropic.ToolInputSchemaParam{
            Type: anthropic.F("object"),
            Properties: map[string]interface{}{
                "location": map[string]string{"type": "string"},
            },
        }),
    }),
}

The response will contain ToolUseBlock elements; execute them and feed results back as ToolResultBlock on the next call.

Cost in Go services

Wrap calls in middleware that records Usage.InputTokens, Usage.OutputTokens, Usage.CacheCreationInputTokens, and Usage.CacheReadInputTokens from every response. Multiply by the model's per-MTok rates to get cost-per-request. Estimate workload cost ahead of time with the Claude Cost Calculator.

For TypeScript and Python equivalents see TypeScript SDK and Python SDK.

Frequently asked questions

Free tools

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