API (Application Programming Interface)

Think of a restaurant menu. You do not walk into the kitchen; you order from a fixed list, in a format the kitchen understands, and food comes back. An API works the same way for software. A weather app does not run its own satellites. It sends a request like “forecast for Seattle” to a weather service’s API and gets back structured data it can display.

The U.S. National Institute of Standards and Technology describes an API as an access point with “well-defined syntax” that programs use to get “well-defined functionality” (NIST). The key idea is the contract: the provider promises that a request in a certain shape gets a response in a certain shape, so the two sides can be built by different teams without knowing each other’s internals.

This is how most AI products reach a model. A customer-support app, a coding assistant or a spreadsheet plugin usually does not run the model itself. Its code sends an HTTP request to a provider such as Anthropic or OpenAI with an API key, the model name and the conversation so far, and the provider returns the model’s reply (Claude API documentation). Settings like temperature and limits on output tokens travel in the same request, and the provider usually bills per token. Agents use APIs in the other direction too: through tool use, a model asks the surrounding program to call an API, such as a calendar or a database, on its behalf. The Model Context Protocol is one standard way to describe those tools to a model.

Two episodes show why the concept matters on the show. In episode 5 at 2:00, Galileo CEO Vikram Chatterji says some 30 million developers “can just invoke these LLMs with just an API call,” which is why software engineers suddenly need evaluation habits that used to belong to data scientists. Galileo sponsored Season 1, when Conor worked there; the episode’s Galileo read is at 20:00. In episode 63 at 2:20, Dhruv Batra argues the opposite limit: most websites, like a city’s tennis-court booking page, will not add APIs for agents any time soon, because “infrastructure takes extremely long to evolve and change.” That is the case for computer use, where an agent operates the human interface instead.

People often say “API” loosely to mean “the paid way to use a model from code,” as opposed to the chat app. That usage is fine; just remember the API is the interface, not the model behind it.