Your First API Call

🟢Beginner

✅

Last verified: 2026-06-20.

The API shape below is stable, but model IDs and SDK versions move. See the current models table.

Confirm against the official source.

The API lets your program talk to Claude. Three steps: get a key, install the SDK, send a message.

1. Get an API key

Create one in the Anthropic Console. Then set it as an environment variable so it never lives in your code:

export ANTHROPIC_API_KEY="sk-ant-..."

:::warning Never commit your key Keep keys in environment variables or a secrets manager — never in source control. See Security. :::

2. Install the SDK

Python

pip install anthropic

TypeScript

npm install @anthropic-ai/sdk

cURL

Nothing to install — you just need curl.

3. Make the call

Every request is a list of messages. The model replies with content.

Python

import anthropic

client = anthropic.Anthropic()  # reads ANTHROPIC_API_KEY from the environment

message = client.messages.create(
    model="claude-sonnet-4-6",
    max_tokens=1024,
    messages=[
        {"role": "user", "content": "In one sentence, what is an API?"}
    ],
)

print(message.content[0].text)

TypeScript

import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic(); // reads ANTHROPIC_API_KEY from the environment

const message = await client.messages.create({
  model: "claude-sonnet-4-6",
  max_tokens: 1024,
  messages: [
    { role: "user", content: "In one sentence, what is an API?" },
  ],
});

console.log(message.content[0].text);

cURL

curl https://api.anthropic.com/v1/messages \
  --header "x-api-key: $ANTHROPIC_API_KEY" \
  --header "anthropic-version: 2023-06-01" \
  --header "content-type: application/json" \
  --data '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 1024,
    "messages": [
      {"role": "user", "content": "In one sentence, what is an API?"}
    ]
  }'

What just happened

• model — which Claude to use. Don't hard-code blindly; see Choosing a Model.
• max_tokens — a cap on the reply length (in tokens). It does not set the context window.
• messages — the conversation so far. The API is stateless: to continue a chat, send the whole history back each time.
• system (optional) — a top-level instruction that sets Claude's role for the call.

Next

• Pick the right model & estimate cost → Choosing a Model · Tokens & Pricing
• Stream responses and hold a conversation → Streaming & Multi-Turn
• Let Claude call your functions → Tool Use
• Production-ready snippets → API Snippets