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Count tokens through agentgateway using the Anthropic Messages token-count API.

The Anthropic token-count API (/v1/messages/count_tokens) estimates the number of input tokens in an Anthropic Messages request before sending it to a model.

About

Agentgateway supports the Anthropic Messages token-count endpoint with the anthropicTokenCount route type. Use this endpoint when clients need to estimate request size before calling /v1/messages, such as to enforce budgets, avoid context-window limits, or show usage estimates.

Route type configuration

In the simplified llm configuration, agentgateway automatically maps /v1/messages/count_tokens requests to the anthropicTokenCount route type, so no explicit route configuration is required.

# yaml-language-server: $schema=https://agentgateway.dev/schema/config
llm:
  models:
  - name: "*"
    provider: anthropic
    params:
      apiKey: "$ANTHROPIC_API_KEY"

To configure the route type explicitly, use the gateways and routes format and set the anthropicTokenCount route type in the policies.ai.routes map. Most configurations also map /v1/messages to the messages route type for the actual model request.

# yaml-language-server: $schema=https://agentgateway.dev/schema/config
gateways:
  default:
    port: 4000
routes:
- backends:
  - ai:
      name: anthropic
      provider:
        anthropic: {}
  policies:
    ai:
      routes:
        "/v1/messages": "messages"
        "/v1/messages/count_tokens": "anthropicTokenCount"
    backendAuth:
      key: "$ANTHROPIC_API_KEY"

Using the API

Send a request to the /v1/messages/count_tokens endpoint with the same message shape that you would send to /v1/messages.

curl 'http://localhost:4000/v1/messages/count_tokens' \
--header 'Content-Type: application/json' \
--data '{
  "model": "claude-opus-4-6",
  "messages": [
    {
      "role": "user",
      "content": "How many tokens are in this request?"
    }
  ]
}'

For Anthropic-specific features such as Messages, token counting, extended thinking, and structured outputs, see the Anthropic provider guide.