What is AI agent?

An AI agent is a program that pursues a goal by taking actions — calling tools and APIs, reading results, and deciding what to do next — with little or no human steering. To use paid resources, an agent needs a way to pay programmatically.

Agent runtimes increasingly treat payment as a first-class capability: given a 402 challenge, the runtime funds, signs, and attaches proof so the agent’s own code just “calls the API and pays if asked.”