Anthropic

Anthropic provider for GoAI - Claude models via the Messages API with native SSE streaming.

Setup

go get github.com/zendev-sh/goai@latest

Set the ANTHROPIC_API_KEY environment variable, or pass it explicitly:

import "github.com/zendev-sh/goai/provider/anthropic"

model := anthropic.Chat("claude-sonnet-4-20250514", anthropic.WithAPIKey("sk-ant-..."))

The provider also reads ANTHROPIC_BASE_URL from the environment when no explicit base URL is set.

Models

Model ID	Type	Notes
claude-opus-4-6-20260310	Chat	Latest Opus, supports native output_format
claude-sonnet-4-6-20260310	Chat	Latest Sonnet, supports native output_format
claude-opus-4-5-20250520	Chat	Supports native output_format
claude-sonnet-4-5-20241022	Chat	Supports native output_format
claude-opus-4-1-20250805	Chat	Supports native output_format
claude-sonnet-4-20250514	Chat	Standard Sonnet
claude-haiku-3-5-20241022	Chat	Fastest Claude model

Tested Models

Unit tested with mock HTTP server (100% coverage). Last run: 2026-03-15.

Model	Generate	Stream	Status
claude-sonnet-4-20250514	PASS	PASS	Stable
claude-sonnet-4-5-20241022	PASS	PASS	Stable
claude-sonnet-4-6-20260310	PASS	PASS	Via Bedrock/Azure E2E

Claude models are also E2E tested via Azure (claude-opus-4-6, claude-sonnet-4-6) and Bedrock (4 Claude cross-region variants: us, eu, global, bare).

Usage

Chat

import (
    "context"
    "fmt"

    "github.com/zendev-sh/goai"
    "github.com/zendev-sh/goai/provider/anthropic"
)

func main() {
    model := anthropic.Chat("claude-sonnet-4-20250514")
    result, err := goai.GenerateText(context.Background(), model,
        goai.WithPrompt("Explain Go interfaces in one paragraph."),
    )
    if err != nil {
        panic(err)
    }
    fmt.Println(result.Text)
}

Streaming

import (
    "context"
    "fmt"

    "github.com/zendev-sh/goai"
    "github.com/zendev-sh/goai/provider"
    "github.com/zendev-sh/goai/provider/anthropic"
)

model := anthropic.Chat("claude-sonnet-4-20250514")
stream, err := goai.StreamText(context.Background(), model,
    goai.WithPrompt("Write a haiku about Go."),
)
if err != nil {
    panic(err)
}
for chunk := range stream.Stream() {
    if chunk.Type == provider.ChunkText {
        fmt.Print(chunk.Text)
    }
}

Extended Thinking

result, err := goai.GenerateText(ctx, model,
    goai.WithPrompt("Solve this step by step: What is 127 * 43?"),
    goai.WithProviderOptions(map[string]any{
        "thinking": map[string]any{
            "type":         "enabled",
            "budgetTokens": 8192,
        },
    }),
)

Thinking types: "enabled" (with budgetTokens), "adaptive", "disabled".

Options

Option	Type	Description
WithAPIKey(key)	string	Static API key. Falls back to ANTHROPIC_API_KEY env var.
WithTokenSource(ts)	provider.TokenSource	Dynamic token resolution.
WithBaseURL(url)	string	Override base URL. Falls back to ANTHROPIC_BASE_URL env var.
WithHeaders(h)	map[string]string	Additional HTTP headers on every request.
WithHTTPClient(c)	*http.Client	Custom HTTP client for proxies, logging, URL rewriting.

Provider Options (via goai.WithProviderOptions)

Key	Type	Description
thinking	map[string]any	Extended thinking config: {type, budgetTokens}.
disableParallelToolUse	bool	Disable parallel tool calls.
effort	string	Output quality level: "low", "medium", "high", "max".
speed	string	Inference speed: "fast", "standard".
structuredOutputMode	string	"outputFormat" for native JSON Schema, "auto" for auto-detect.
container	map[string]any	Code execution container: {id, skills}.
contextManagement	map[string]any	Automatic context window management edits.

Provider Tools

Ten built-in tools are available via anthropic.Tools. These use Anthropic's native tool types.

Tool	Version	Description	Execution
anthropic.Tools.Computer()	20250124	Screenshot, mouse/keyboard control	Client-side
anthropic.Tools.Computer_20251124()	20251124	Computer use with zoom support	Client-side
anthropic.Tools.Bash()	20250124	Execute bash commands	Client-side
anthropic.Tools.TextEditor()	20250429	View/edit files (str_replace)	Client-side
anthropic.Tools.TextEditor_20250728()	20250728	Text editor with maxCharacters	Client-side
anthropic.Tools.WebSearch()	20250305	Web search via Brave Search	Server-side
anthropic.Tools.WebSearch_20260209()	20260209	Updated web search	Server-side
anthropic.Tools.WebFetch()	20260209	Fetch URL content	Server-side
anthropic.Tools.CodeExecution()	20260120	Server-side Python execution	Server-side
anthropic.Tools.CodeExecution_20250825()	20250825	Earlier code execution version	Server-side

Computer Use

Computer use tools require client-side execution. The model generates actions (click, type, screenshot), and your application executes them and returns results.

def := anthropic.Tools.Computer(anthropic.ComputerToolOptions{
    DisplayWidthPx:  1920,
    DisplayHeightPx: 1080,
})
result, err := goai.GenerateText(ctx, model,
    goai.WithPrompt("Open the browser and navigate to example.com"),
    goai.WithTools(goai.Tool{
        Name:                   def.Name,
        ProviderDefinedType:    def.ProviderDefinedType,
        ProviderDefinedOptions: def.ProviderDefinedOptions,
    }),
)
// Handle tool calls in result.ToolCalls - execute actions and return results

The Computer_20251124 version adds zoom support for Opus 4.5+:

def := anthropic.Tools.Computer_20251124(anthropic.Computer20251124Options{
    DisplayWidthPx:  1920,
    DisplayHeightPx: 1080,
    EnableZoom:      true,
})
result, err := goai.GenerateText(ctx, model,
    goai.WithPrompt("Take a zoomed screenshot of the top-left corner"),
    goai.WithTools(goai.Tool{
        Name:                   def.Name,
        ProviderDefinedType:    def.ProviderDefinedType,
        ProviderDefinedOptions: def.ProviderDefinedOptions,
    }),
)

Bash and TextEditor

bashDef := anthropic.Tools.Bash()
editorDef := anthropic.Tools.TextEditor()
result, err := goai.GenerateText(ctx, model,
    goai.WithPrompt("List files in the current directory"),
    goai.WithTools(
        goai.Tool{Name: bashDef.Name, ProviderDefinedType: bashDef.ProviderDefinedType, ProviderDefinedOptions: bashDef.ProviderDefinedOptions},
        goai.Tool{Name: editorDef.Name, ProviderDefinedType: editorDef.ProviderDefinedType, ProviderDefinedOptions: editorDef.ProviderDefinedOptions},
    ),
)

TextEditor_20250728 supports an optional character limit:

def := anthropic.Tools.TextEditor_20250728(anthropic.WithMaxCharacters(100000))
result, err := goai.GenerateText(ctx, model,
    goai.WithPrompt("Open main.go and fix the syntax error"),
    goai.WithTools(goai.Tool{
        Name:                   def.Name,
        ProviderDefinedType:    def.ProviderDefinedType,
        ProviderDefinedOptions: def.ProviderDefinedOptions,
    }),
)

WebSearch

def := anthropic.Tools.WebSearch(
    anthropic.WithMaxUses(5),
    anthropic.WithAllowedDomains("go.dev", "github.com"),
)
result, err := goai.GenerateText(ctx, model,
    goai.WithPrompt("What are the latest developments in Go 1.25?"),
    goai.WithTools(goai.Tool{
        Name:                   def.Name,
        ProviderDefinedType:    def.ProviderDefinedType,
        ProviderDefinedOptions: def.ProviderDefinedOptions,
    }),
)

Options: WithMaxUses(n), WithAllowedDomains(...), WithBlockedDomains(...), WithWebSearchUserLocation(...).

WebFetch

def := anthropic.Tools.WebFetch(
    anthropic.WithCitations(true),
    anthropic.WithMaxContentTokens(4096),
)
result, err := goai.GenerateText(ctx, model,
    goai.WithPrompt("Summarize the content at https://go.dev/blog"),
    goai.WithTools(goai.Tool{
        Name:                   def.Name,
        ProviderDefinedType:    def.ProviderDefinedType,
        ProviderDefinedOptions: def.ProviderDefinedOptions,
    }),
)

Options: WithWebFetchMaxUses(n), WithWebFetchAllowedDomains(...), WithWebFetchBlockedDomains(...), WithCitations(bool), WithMaxContentTokens(n).

CodeExecution

def := anthropic.Tools.CodeExecution()
result, err := goai.GenerateText(ctx, model,
    goai.WithPrompt("Calculate the standard deviation of [4, 8, 15, 16, 23, 42]"),
    goai.WithTools(goai.Tool{
        Name:                   def.Name,
        ProviderDefinedType:    def.ProviderDefinedType,
        ProviderDefinedOptions: def.ProviderDefinedOptions,
    }),
)

Notes

• Prompt caching: When goai.WithPromptCaching(true) is set, the system prompt receives cache_control: {type: "ephemeral"}. Message-level caching is controlled via ProviderOptions["anthropic"]["cacheControl"] on the message, or via Part.CacheControl on individual content parts.
• Structured output: Anthropic does not natively support JSON Schema response_format on all models. GoAI uses a synthetic tool injection pattern - a hidden tool with the schema is injected, and the model is forced to call it. For Claude Opus 4.1+, Sonnet 4.5+, Opus 4.5+, Sonnet 4.6, and Opus 4.6, set structuredOutputMode: "outputFormat" to use native output_format instead.
• Beta headers: Provider-defined tools automatically add the required anthropic-beta header values. The base beta features (claude-code-20250219, interleaved-thinking-2025-05-14) are always included.
• Default max tokens: 16384 when not explicitly set via goai.WithMaxOutputTokens().
• Auth header: Uses x-api-key (not Authorization: Bearer), matching Anthropic's API convention.
• Input modalities: Supports text, images (base64), and PDF documents (base64).
• File upload: Anthropic supports remote file upload via the Files API. Use model.FileUploader() to get a provider.FileUploader for uploading and deleting files. Uploaded files are referenced via Part.RemoteRef in messages. Compat providers map file parts to native OpenAI shapes (file for PDFs, input_audio for audio).