Question

A developer is building a chatbot and wants to display an estimated cost to users before sending each request to the Messages API. They need to know how many input tokens a given prompt (system prompt plus conversation history) will consume, without actually generating a response and being billed for output. What is the most appropriate approach?

Accepted Answer

Use the token counting endpoint to count the input tokens for the messages and system prompt before sending the generation request

Answer

Send the request with max_tokens set to 0 so the model returns only the input token count without generating output

Answer

Divide the total number of characters in the prompt by 4 and treat that as the exact billed token count

Answer

Enable streaming and read the token usage from the first streamed event before any output tokens are produced