How does File Search work in the Responses API, and what is its pricing?

Hey guys,
I created an agent using the Responses API with GPT-4.1 Mini, and it’s going well, but I noticed something strange in consumption:
• Around 7k tokens per message
• And 22k tokens per search on File Search + Message. I’ve tried with smaller files and the cost remains the same

Can anyone explain how token calculation works in File Search?