Spend $0 to Count Claude Input Tokens

2026-10-29 Spend less EN

When every paid API call matters, do not guess how large your prompt is. Anthropic’s token counting endpoint lets you estimate the input tokens for a Claude request before sending it to the Messages API. Anthropic currently provides this counting endpoint without charging for the count. That does not make the model request free: the later generation is billed separately.

01 / Count the input before paying for a reply

The endpoint is /v1/messages/count_tokens on Anthropic’s API. Send it the model and the same input structure you intend to use for a message request. It responds with an input_tokens value. This is an input estimate, not a quote for the whole interaction: generated output is not included, and your final bill depends on the actual request and model pricing.

Here is a minimal command-line example. Replace the model name with one available to your account, and set your key in the environment rather than pasting it into a shared script:

curl https://api.anthropic.com/v1/messages/count_tokens -H "x-api-key: $ANTHROPIC_API_KEY" -H "anthropic-version: 2023-06-01" -H "content-type: application/json" -d '{"model":"claude-haiku-4-5","messages":[{"role":"user","content":"Summarize this short note in three bullets."}]}'

A successful response contains a count such as {"input_tokens": 18}. Treat that number as an example of response shape, not a promised count for every account or model. Your actual prompt, selected model, and supported request features determine the result.

02 / Match the request you plan to send

Counting a tiny test prompt and then sending a much larger one tells you almost nothing about the larger call. Include the real system instructions, conversation history, and user content when you count. If you use tools, images, or other structured content, follow the endpoint’s current documentation for the accepted format and include those parts too. Keep the counting request aligned with the paid request you will actually make.

For a tight budget, start with the prompt you need today. Avoid counting every draft while you are still editing; make the wording changes first, then count the final version. Save the result beside the prompt if you reuse it, and recount after changing the model or content. A token count is not a guarantee that two different model requests cost the same amount.

03 / Turn a count into a budget check

To estimate input cost, multiply the counted input tokens by that model’s published input price per token. If the price is listed per million tokens, divide the token count by 1,000,000 before multiplying. Add a separate allowance for output tokens, which you control partly with the maximum output setting but cannot know exactly in advance. Check current prices before calculating; model rates can differ and change.

■ Count input tokens before sending the paid generation request.
■ Estimate output separately; the count endpoint does not predict how many tokens the model will generate.
■ Check whether your request uses prompt caching or other billable token categories. A plain input count is not a complete invoice.
■ Do not assume the endpoint is available through every API relay. Anthropic’s endpoint and a provider’s OpenAI-compatible routes are different interfaces.

04 / Keep the counting route separate from relay billing

CheapRelay offers pay-as-you-go access through its API base at https://api.cheapapirelay.com, with OpenAI-compatible routes under /v1 and Gemini’s native API under /v1beta. Its published interface does not establish that Anthropic’s native /v1/messages/count_tokens route is available there. Use Anthropic’s documented endpoint for this counting workflow unless CheapRelay documents support for that exact route.

For paid calls routed through CheapRelay, billing is per real token, including cache reads and writes, with no monthly fee or subscription. That can help keep spending tied to use, but it does not replace checking model prices or setting a practical output limit. Sign up for CheapRelay if you want to route supported model calls through one pay-as-you-go account; keep the token-counting request on the API that explicitly supports it.

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