What is the difference between an AI agent, a workflow and a script?

A script is a program with a fixed, hard-coded procedure: it does the same thing every time and never improvises. A workflow is a predefined sequence of steps in which the model handles one part – for example it reads an e-mail and converts it into structured data. An agent is given a goal and a set of tools and chooses the order of steps itself, based on what it discovers along the way. Each of the three architectures has a different price, speed and level of predictability, so the choice is not cosmetic.