API overview

The Claude API is a RESTful API at https://api.anthropic.com that provides programmatic access to Claude models and Claude Managed Agents.

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Prerequisites

To use the Claude API, you'll need:

• A Claude Console account
• An API key, or a configured Workload Identity Federation rule

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

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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)
• Agents API: Define reusable, versioned agent configurations for Claude Managed Agents (POST /v1/agents, GET /v1/agents)
• Sessions API: Run stateful agent sessions in managed cloud sandboxes (POST /v1/sessions, GET /v1/sessions/{id}/stream)
• Environments API: Configure sandbox templates for agent sessions (POST /v1/environments, GET /v1/environments)

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.

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Authentication

For details on both authentication methods and when to use each, see 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.

When accessing Claude through a cloud platform, authentication is integrated with the cloud provider's IAM system. See the platform-specific documentation for supported credential types, required headers, and authentication options.

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Getting API keys

The API is made available through 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.

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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

For a list of client SDKs, see Client SDKs.

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Claude API vs cloud platforms

Claude is available through the direct Claude API and through cloud platforms. Choose based on your infrastructure, feature availability, compliance requirements, and pricing preferences.

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Claude API

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

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Cloud platform APIs

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

• Integrated with cloud provider billing and IAM
• Feature availability varies by platform: Anthropic-operated platforms include Claude Platform on AWS and Microsoft Foundry; partner-operated platforms include Amazon Bedrock and Google Cloud. See each platform's page for feature availability and timing.
• Best for: Existing cloud commitments, specific compliance requirements, consolidated cloud billing

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Request and response format

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Request size limits

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

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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

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Pagination

List endpoints return results in pages. Most newer list endpoints use the page and next_page cursor scheme described in this section. Some use a different scheme; see the note at the end of this section. Use the limit query parameter to control the page size and the page query parameter to fetch an adjacent page. Each response includes a data array alongside cursor fields for navigating between pages.

To go back a page, pass prev_page as the page parameter. prev_page is null when you're on the first page. Not all list endpoints support prev_page. Only GET /v1/sessions returns prev_page; on list endpoints that do not support backward pagination, the field is absent from the response rather than null. For a request walkthrough, see Listing sessions.

Every SDK provides an auto-paginating iterator that follows next_page for you. In Python and TypeScript, you get it by iterating the list result directly. The other SDKs provide the iterator through a separate method. SDK auto-pagination is forward-only; to go back a page, read prev_page from the response and pass it back as the page parameter yourself. See client SDKs for language-specific details.

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Rate limits and availability

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Rate limits

The API enforces rate limits and spend limits to prevent misuse and manage capacity. Limits are organized into usage tiers; your organization is placed on a tier automatically and can move to a higher tier over time. 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, use Request rate limit increase on the Limits page.

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

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Availability

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

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Next steps