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🧠 Models and how they work · ⏱️ 2 min Latte

What is API?

Illustration: API
Simply put, like I'm 5 years oldAn API is like a restaurant counter with a menu: you ask for a dish in the right words, the kitchen cooks it, and the food comes back to you, but you never go into the kitchen.

📖 The slightly longer version

API means "application programming interface". It is a door that lets one program talk to another program. A developer's app sends a request in a fixed format, and the service sends back an answer. No human clicks anything. It is software talking to software.

Most AI you meet works this way behind the scenes. A shopping app or a chatbot on a website often does not run its own model. It sends your text to a big AI company's API and shows you the reply. The company usually charges per call (each request) or per token (a small piece of text). Google's new Decisions API, for example, is described as answering up to 1,000 yes/no questions in a single call.

How an app uses an AI API

  1. You use an appYou type a question in a website or app.
  2. App sends requestThe app sends your text to the AI company's API.
  3. Model worksThe company's AI model reads the request and makes an answer.
  4. Answer comes backThe API sends the reply back, and the app shows it to you.
  5. Company billsThe app maker pays per call or per token used.
Why it matters

When Google raises the price of Gemini 4 Carbon and Argon from $2 to $4 per million input tokens on December 1, the apps built on that API pay more. Some of that cost can come back to you, or the app may quietly switch models. Many tools you use every day depend on a few big companies' APIs, so their prices and rules shape what you get.

⚠️ What to watch out for

An API hides what happens inside: you send data out and trust the answer that comes back. Your text may leave your computer and go to a company's servers, so check what an app sends and where. Prices can also be confusing and can change, as Simon Willison noted about the Gemini 4 pricing. If a company changes or shuts down its API, every app built on it can break overnight.

📰 Where it showed up

This notion came up in Nvidia's CEO falls in a spy scandal. Can anyone track where AI chips go?. More lessons: Learn.

🎯 Keep learning

New 🧠 Models and how they work · 2 min Latte What is GPU? A GPU is like a huge kitchen with thousands of cooks, each chopping one small carrot at the same time. One cook alone is slow, but thousands together finish the whole soup very fast. Learn it → New 🧠 Models and how they work · 2 min Latte What is Emulator? An emulator is like a practice kitchen at home that looks just like a big restaurant kitchen, so you can try a new recipe without wasting the restaurant's food. Learn it → New 🧠 Models and how they work · 2 min Cappuccino What is Proof Checker? A proof checker is like a very careful friend who checks every line of a long grocery receipt, one by one. It does not care who wrote the receipt. It only cares if each line adds up. Learn it →

Sources

Written on 2026-11-13. This explanation was accurate on that day. AI changes fast, so check the sources and the date before you rely on it.

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