Anthropic Hello World

Overview

Send your first message to Claude and get a response using the Messages API.

Prerequisites

• Completed clade-install-auth setup
• ANTHROPIC_API_KEY environment variable set

Instructions

Step 1: Basic Message

import Anthropic from '@claude-ai/sdk';

const client = new Anthropic();

const message = await client.messages.create({
  model: 'claude-sonnet-4-20250514',
  max_tokens: 1024,
  messages: [
    { role: 'user', content: 'What is the capital of France?' }
  ],
});

console.log(message.content[0].text);
// "The capital of France is Paris."

Step 2: Add a System Prompt

const message = await client.messages.create({
  model: 'claude-sonnet-4-20250514',
  max_tokens: 1024,
  system: 'You are a helpful geography expert. Be concise.',
  messages: [
    { role: 'user', content: 'What is the capital of France?' }
  ],
});

Step 3: Multi-Turn Conversation

const message = await client.messages.create({
  model: 'claude-sonnet-4-20250514',
  max_tokens: 1024,
  messages: [
    { role: 'user', content: 'What is the capital of France?' },
    { role: 'assistant', content: 'The capital of France is Paris.' },
    { role: 'user', content: 'What is its population?' },
  ],
});

Python Example

import anthropic

client = anthropic.Anthropic()

message = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    messages=[
        {"role": "user", "content": "What is the capital of France?"}
    ],
)
print(message.content[0].text)

Output

• message.content[0].text — Claude's text response
• message.model — model ID used
• message.usage.input_tokens / message.usage.output_tokens — token counts
• message.stop_reason — end_turn, max_tokens, or tool_use

Error Handling

Error	Cause	Solution
authentication_error	Bad API key	Check ANTHROPIC_API_KEY
invalid_request_error	Missing required field	Both messages and max_tokens are required
not_found_error	Invalid model ID	Use a valid model like claude-sonnet-4-20250514

Available Models

Model	Best For	Context	Cost (input/output per MTok)
claude-opus-4-20250514	Complex reasoning	200K	$15 / $75
claude-sonnet-4-20250514	Balanced quality + speed	200K	$3 / $15
claude-haiku-4-5-20251001	Fast, cheap tasks	200K	$0.80 / $4

Examples

See Step 1 (basic message), Step 2 (system prompt), and Step 3 (multi-turn) above. Python example included in its own section.

Resources

• Messages API Reference
• Model Overview

Next Steps

Proceed to clade-model-inference for streaming and advanced patterns.