--- title: Documentation url: https://platform.claude.com/docs/en/home description: Claude API Documentation --- Quickstart Get API key API reference ```python Python import anthropic client = anthropic.Anthropic() message = client.messages.create( model="claude-opus-5-5", max_tokens=1024, messages=[ { "role": "user", "content": "Hello, Claude", } ], ) for block in message.content: if block.type == "text": print(block.text) ``` ```typescript TypeScript import Anthropic from "@anthropic-ai/sdk"; const client = new Anthropic(); const msg = await client.messages.create({ model: "claude-opus-5-5", max_tokens: 1024, messages: [ { role: "user", content: "Hello, Claude" } ] }); for (const block of msg.content) { if (block.type === "text") { console.log(block.text); } } ``` ```go Go import "github.com/anthropics/anthropic-sdk-go" client := anthropic.NewClient() msg, _ := client.Messages.New( context.TODO(), anthropic.MessageNewParams{ Model: anthropic.ModelClaudeOpus5_5, MaxTokens: 1024, Messages: []anthropic.MessageParam{ anthropic.NewUserMessage( anthropic.NewTextBlock("Hello, Claude"), ), }, }, ) for _, block := range msg.Content { if textBlock, ok := block.AsAny().(anthropic.TextBlock); ok { fmt.Println(textBlock.Text) } } ``` ```java Java import com.anthropic.client.okhttp.AnthropicOkHttpClient; var client = AnthropicOkHttpClient .fromEnv(); var msg = client.messages().create( MessageCreateParams.builder() .model("claude-opus-5-5") .maxTokens(1024) .addUserMessage("Hello, Claude") .build() ); for (var block : msg.content()) { block.text().ifPresent( textBlock -> System.out.println(textBlock.text())); } ``` ```ruby Ruby require "anthropic" client = Anthropic::Client.new msg = client.messages.create( model: "claude-opus-5-5", max_tokens: 1024, messages: [{ role: "user", content: "Hello, Claude" }] ) msg.content.each do |block| puts block.text if block.type == :text end ``` ```php PHP use Anthropic\Client; $client = new Client(); $message = $client->messages->create( model: "claude-opus-5-5", maxTokens: 1024, messages: [['role' => 'user', 'content' => 'Hello, Claude']], ); foreach ($message->content as $block) { if ($block->type === 'text') { echo $block->text, PHP_EOL; } } ``` ```csharp C# using Anthropic; var client = new AnthropicClient(); var msg = await client.Messages .Create(new() { Model = "claude-opus-5-5", MaxTokens = 1024, Messages = [new() { Role = Role.User, Content = "Hello, Claude" }] }); foreach (var block in msg.Content) { if (block.TryPickText(out var textBlock)) { Console.WriteLine(textBlock.Text); } } ``` ```bash cURL curl https://api.anthropic.com/v1/messages \ -H "content-type: application/json" \ -H "x-api-key: $ANTHROPIC_API_KEY" \ -H "anthropic-version: 2023-06-01" \ -d '{ "model": "claude-opus-5-5", "max_tokens": 1024, "messages": [{ "role": "user", "content": "Hello, Claude" }] }' ``` ```bash CLI ant messages create \ --model claude-opus-5-5 \ --max-tokens 1024 \ --message '{ role: user, content: "Hello, Claude" }' ``` Quickstart API reference Client SDKs Quickstart API reference Define your agent Amazon Bedrock Google Cloud Microsoft Foundry Quickstart Get API key Choose a model Install an SDK Try the API in playground Messages API Thinking Vision Tool use Web search Code execution Structured outputs Prompt caching Streaming Prompting best practices Run evals Batch testing Safety and guardrails Rate limits and errors Cost optimization Workspaces and admin API key management Usage monitoring Model migration Quickstart Get API key Build in Console Agent setup Tools Tool permissions Streaming and events Sessions API reference Workspaces and admin API key management Usage monitoring * [Claude Fable 5.1](https://platform.claude.com/docs/en/models/fable-5-1/overview) (`claude-fable-5-1`) — New — *For demanding reasoning and long-horizon agentic work* — Most capable · Research · Multi-day tasks * [Claude Opus 5.5](https://platform.claude.com/docs/en/models/opus-5-5/overview) (`claude-opus-5-5`) — New — *For long-running agentic coding and knowledge work* — Complex projects · Agents · Coding * [Claude Sonnet 5.5](https://platform.claude.com/docs/en/models/sonnet-5-5/overview) (`claude-sonnet-5-5`) — New — *The best combination of speed and intelligence* — Everyday tasks · Writing · Cost-efficient * [Claude Haiku 5.5](https://platform.claude.com/docs/en/models/haiku-5-5/overview) (`claude-haiku-5-5`) — New — *For high-volume, latency-sensitive tasks such as classification, extraction, and routing* — Fastest · Lowest cost · High volume Interactive courses to master Claude. Code samples and patterns. Deployable starter apps. Latest features and updates. An agentic coding assistant in your terminal.