Arcflow exposes POST /v1/messages/count_tokens, which forwards to Anthropic with the token-counting beta header. Use it to estimate context size before you send a request. Claude models only.

The body is a Messages request without max_tokens:

curl https://api.tryarcflow.com/v1/messages/count_tokens \
  -H "Authorization: Bearer sk-..." \
  -H "anthropic-version: 2023-06-01" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4-6",
    "messages": [{ "role": "user", "content": "How many tokens is this?" }]
  }'

The response reports the input token count:

{ "input_tokens": 14 }

Use this to estimate context before sending a full Messages request, for example to stay within a model's context window or to predict usage.

Token Counting