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Proxy Anthropic Requests

Anthropic provides the native Messages API and an OpenAI-compatible API for accessing Claude models.

This guide shows how to integrate APISIX with Anthropic using the ai-proxy plugin. With provider set to anthropic, you do not need to set a custom endpoint.

Prerequisite(s)​

  • Install Docker.
  • Install cURL to send requests to the services for validation.
  • Follow the Getting Started Tutorial to start a new APISIX instance in Docker or on Kubernetes.

Obtain an Anthropic API Key​

Create an account and API key by following the Anthropic API Documentation. Optionally save the key to an environment variable:

export ANTHROPIC_API_KEY=sk-ant-xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx  # replace with your API key

Create a Route to Anthropic​

This example accepts an OpenAI Chat Completions request on a custom path. APISIX identifies the format from the messages field and sends it to Anthropic's OpenAI-compatible endpoint. To accept the native Anthropic Messages format instead, configure a route URI ending in /v1/messages; see Native Anthropic Messages API Pass-Through.

Create a route with the ai-proxy plugin as such:

curl "http://127.0.0.1:9180/apisix/admin/routes" -X PUT \
  -H "X-API-KEY: ${ADMIN_API_KEY}" \
  --data-binary @- <<EOF
{
  "id": "anthropic-chat",
  "uri": "/anything",
  "plugins": {
    "ai-proxy": {
      "provider": "anthropic",
      "auth": {
        "header": {
          "x-api-key": "$ANTHROPIC_API_KEY"
        }
      },
      "options": {
        "model": "claude-sonnet-4-5"
      }
    }
  }
}
EOF

❶ Set the provider to anthropic.

❷ Attach the Anthropic API key using the x-api-key header.

❸ Set a model supported by Anthropic, for example claude-sonnet-4-5.

Verify​

Send a request with the following prompts to the route:

curl "http://127.0.0.1:9080/anything" -X POST \
  -H "Content-Type: application/json" \
  -d '{"messages": [{"role": "user", "content": "Hello"}]}'

You should receive a response similar to the following:

{
  "request": {
    "messages": [
      {
        "role": "user",
        "content": "Hello"
      }
    ]
  },
  "response": {
    "id": "msg_01HUQ8fAR1XvJ9PodefrZixW",
    "object": "chat.completion",
    "created": 1770029318,
    "model": "claude-sonnet-4-5-20250929",
    "choices": [
      {
        "index": 0,
        "finish_reason": "stop",
        "message": {
          "role": "assistant",
          "content": "Hello! How can I help you today?"
        }
      }
    ],
    "usage": {
      "prompt_tokens": 8,
      "completion_tokens": 12,
      "total_tokens": 20
    }
  }
}

Proxy Native Anthropic Messages​

When the client and Anthropic both use the Messages API, configure a route ending in /v1/messages. APISIX detects the path and forwards the native request without protocol conversion, preserving Anthropic-specific request and response fields.

Create a native Messages route:

curl "http://127.0.0.1:9180/apisix/admin/routes" -X PUT \
  -H "X-API-KEY: ${ADMIN_API_KEY}" \
  --data-binary @- <<EOF
{
  "id": "anthropic-messages",
  "uri": "/v1/messages",
  "plugins": {
    "ai-proxy": {
      "provider": "anthropic",
      "auth": {
        "header": {
          "x-api-key": "$ANTHROPIC_API_KEY"
        }
      },
      "options": {
        "model": "claude-sonnet-4-5"
      }
    }
  }
}
EOF

Send a native Messages request:

curl "http://127.0.0.1:9080/v1/messages" -X POST \
  -H "Content-Type: application/json" \
  -H "anthropic-version: 2023-06-01" \
  -d '{
    "max_tokens": 128,
    "messages": [
      {
        "role": "user",
        "content": "Hello"
      }
    ]
  }'

You should receive a native Anthropic Messages response similar to the following:

{
  "id": "msg_01HUQ8fAR1XvJ9PodefrZixW",
  "type": "message",
  "role": "assistant",
  "model": "claude-sonnet-4-5-20250929",
  "content": [
    {
      "type": "text",
      "text": "Hello! How can I help you today?"
    }
  ],
  "stop_reason": "end_turn",
  "stop_sequence": null,
  "usage": {
    "input_tokens": 8,
    "output_tokens": 12
  }
}

To verify streaming, send a request with stream set to true. The -N option disables curl response buffering so that each event is displayed as it arrives:

curl -N "http://127.0.0.1:9080/v1/messages" -X POST \
  -H "Content-Type: application/json" \
  -H "anthropic-version: 2023-06-01" \
  -d '{
    "max_tokens": 128,
    "stream": true,
    "messages": [
      {
        "role": "user",
        "content": "Hello"
      }
    ]
  }'

You should receive Anthropic SSE events ending with message_stop, similar to the following abbreviated response:

event: message_start
data: {"type":"message_start","message":{"type":"message","role":"assistant",...}}

event: content_block_delta
data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"Hello"}}

...

event: message_stop
data: {"type":"message_stop"}

Next Steps​

You have learned how to integrate APISIX with Anthropic. See the Anthropic API Documentation and Models pages for more details.