How to Fix Claude API 404 Not Found Error

An HTTP 404 Not Found or 404 Resource Not Found error occurs when your application sends a request to a URL path that the Anthropic server cannot resolve. This is almost never a problem with Claude itself; instead, it is a configuration mismatch between your code, SDK parameters, or endpoint paths.

When using the Claude API, 404 errors typically point to three primary issues: an outdated API base URL in your SDK configuration, a typo in the resource endpoint, or requesting a model that has been completely deprecated and removed from the active routing tables.

Follow these troubleshooting steps to locate and resolve the 404 error in your application.

Step 1: Verify and Reset the API Base URL

If you use third-party frameworks, proxy configurations, or run local API wrappers (such as LiteLLM, LangChain, or custom local gateways), the client may be routing requests to an incorrect base address.

The default base URL for all official Claude API endpoints must be set exactly as follows:

` https://api.anthropic.com `

If you have customized the client instantiation in your code, verify you did not append extra path segments to the host parameter. For example, in Python:

`python # INCORRECT - Will cause a 404 error because /v1 is appended to the base from anthropic import Anthropic client = Anthropic( base_url="https://api.anthropic.com/v1", api_key="your_key" )

CORRECT - The official SDK appends paths automatically from anthropic import Anthropic client = Anthropic( base_url="https://api.anthropic.com", api_key="your_key" ) ```

When using manual HTTP requests, the base URL must target https://api.anthropic.com, and individual endpoints are appended dynamically.

Step 2: Confirm the Endpoint Path Syntax

Anthropic relies on specific paths for handling inference. If you make a typographical error in the resource path, the server will return a standard 404 HTML/JSON response.

Confirm that your HTTP routing target matches these exact structures:

* Messages API (Standard Claude 3 & 3.5 Models): /v1/messages (e.g., https://api.anthropic.com/v1/messages via POST) * Legacy Text Completions API (Legacy Claude 1 & 2 Models): /v1/complete (e.g., https://api.anthropic.com/v1/complete via POST)

Common syntax mistakes that trigger a 404 include: * Pluralizing the legacy path: /v1/completions (this is an OpenAI path structure, not Anthropic's). * Forgetting the version prefix: /messages instead of /v1/messages. * Including trailing slashes: /v1/messages/.

Step 3: Check for Model Deprecations

If your endpoint structure is pristine but you receive a 404 when referencing a specific model, Anthropic may have decommissioned or renamed that model. While model mismatches usually yield 400 errors, certain custom or legacy routing architectures will trigger a 404 when looking for a resource that no longer exists on the cluster.

Ensure you are using modern, supported model strings in your payload.

• Active Supported Models:
• claude-3-5-sonnet-20241022 (Claude 3.5 Sonnet v2)
• claude-3-5-haiku-20241022 (Claude 3.5 Haiku)
• claude-3-opus-20240229 (Claude 3 Opus)
• claude-3-sonnet-20240229 (Claude 3 Sonnet)
• claude-3-haiku-20240307 (Claude 3 Haiku)

If your system is hardcoded to reference older models like claude-instant-1.2 or raw developer previews, verify they are still supported in your console's workspace dashboard.

Step 4: Inspect Proxy and Gateway Redirections

If you run your code inside an enterprise network, a virtual private cloud (VPC), or route requests through cloud firewalls, your network's outbound reverse proxy may be catching the traffic and failing to map it correctly. This returns a local network 404 instead of a remote 404 from Anthropic.

1. Disable any active VPNs, corporate firewalls, or custom local proxies to test the direct connection. 2. Execute a raw shell test using curl to see if the block is internal: `bash curl -I https://api.anthropic.com/v1/messages ` If this returns a 405 Method Not Allowed response, the server connection is working (since GET is not allowed on that route). If it returns a standard 404 Not Found, your local routing table or security appliance is blocking or misdirecting the external domain.

When to escalate

If you have corrected your endpoints, verified that your base URL is unmodified, and verified that direct curl calls still yield 404 errors, your API workspace may be assigned to a deprecated cluster. Contact Anthropic developer support by logging into your Console, clicking the support bubble, and sharing your code implementation block and destination server region details.