API Overview

The Claude API is a RESTful API at https://api.anthropic.com that provides programmatic access to Claude models. The primary API is the Messages API (POST /v1/messages) for conversational interactions.

Prerequisites

To use the Claude API, you'll need:

• An Anthropic Console account
• An API key

For step-by-step setup instructions, see Get started.

Available APIs

The Claude API includes the following APIs:

General Availability:

• Messages API: Send messages to Claude for conversational interactions (POST /v1/messages)
• Message Batches API: Process large volumes of Messages requests asynchronously with 50% cost reduction (POST /v1/messages/batches)
• Token Counting API: Count tokens in a message before sending to manage costs and rate limits (POST /v1/messages/count_tokens)
• Models API: List available Claude models and their details (GET /v1/models)

Beta:

• Files API: Upload and manage files for use across multiple API calls (POST /v1/files, GET /v1/files)
• Skills API: Create and manage custom agent skills (POST /v1/skills, GET /v1/skills)

For the complete API reference with all endpoints, parameters, and response schemas, explore the API reference pages listed in the navigation. To access beta features, see Beta headers.

Authentication

All requests to the Claude API must include these headers:

If you are using the Client SDKs, the SDK will send these headers automatically. For API versioning details, see API versions.

Getting API Keys

The API is made available via the web Console. You can use the Workbench to try out the API in the browser and then generate API keys in Account Settings. Use workspaces to segment your API keys and control spend by use case.

Client SDKs

Anthropic provides official SDKs that simplify API integration by handling authentication, request formatting, error handling, and more.

Benefits:

• Automatic header management (x-api-key, anthropic-version, content-type)
• Type-safe request and response handling
• Built-in retry logic and error handling
• Streaming support
• Request timeouts and connection management

Example (Python):

from anthropic import Anthropic

client = Anthropic()  # Reads ANTHROPIC_API_KEY from environment
message = client.messages.create(
    model="claude-sonnet-4-5",
    max_tokens=1024,
    messages=[{"role": "user", "content": "Hello, Claude"}]
)

For a list of client SDKs and their respective installation instructions, see Client SDKs.

Claude API vs Third-Party Platforms

Claude is available through Anthropic's direct API and through partner platforms. Choose based on your infrastructure, compliance requirements, and pricing preferences.

Claude API

• Direct access to the latest models and features first
• Anthropic billing and support
• Best for: New integrations, full feature access, direct relationship with Anthropic

Third-Party Platform APIs

Access Claude through AWS, Google Cloud, or Microsoft Azure:

• Integrated with cloud provider billing and IAM
• May have feature delays or differences from the direct API
• Best for: Existing cloud commitments, specific compliance requirements, consolidated cloud billing

Request and Response Format

Request Size Limits

The API has different maximum request sizes depending on the endpoint:

If you exceed these limits, you'll receive a 413 request_too_large error.

Response Headers

The Claude API includes the following headers in every response:

• request-id: A globally unique identifier for the request
• anthropic-organization-id: The organization ID associated with the API key used in the request

Rate Limits and Availability

Rate Limits

The API enforces rate limits and spend limits to prevent misuse and manage capacity. Limits are organized into usage tiers that increase automatically as you use the API. Each tier has:

• Spend limits: Maximum monthly cost for API usage
• Rate limits: Maximum number of requests per minute (RPM) and tokens per minute (TPM)

You can view your organization's current limits in the Console. For higher limits or Priority Tier (enhanced service levels with committed spend), contact sales through the Console.

For detailed information about limits, tiers, and the token bucket algorithm used for rate limiting, see Rate limits.

Availability

The Claude API is available in many countries and regions worldwide. Check the supported regions page to confirm availability in your location.

Basic Example

Here's a minimal request using the Messages API:

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-4-5",
    "max_tokens": 1024,
    "messages": [
      {"role": "user", "content": "Hello, Claude"}
    ]
  }'

Response:

{
  "id": "msg_01XFDUDYJgAACzvnptvVoYEL",
  "type": "message",
  "role": "assistant",
  "content": [
    {
      "type": "text",
      "text": "Hello! How can I assist you today?"
    }
  ],
  "model": "claude-sonnet-4-5",
  "stop_reason": "end_turn",
  "usage": {
    "input_tokens": 12,
    "output_tokens": 8
  }
}

For complete examples and tutorials, see Get started and Working with Messages.

Next Steps