AI agent.

An AI agent is an AI you hand real work to. The cleanest way to think about it: a Chat model is question to answer, an agent is goal to result. The word "agent" comes from agency, the capacity to do things and take action. So instead of asking ChatGPT a question and then going off to do the work yourself, you give a model tools, memory, and the ability to act, and it goes and does the work for you. It plans, breaks the goal into its own to-do list, and runs until the job is done.

Think of it like a great employee you've hired full-time who actually goes and does the work, not a consultant you ask and then have to act on yourself.

For builders, this is the whole change. Once a model has tools and can loop, the question moves from "what's the best prompt" to "what's the goal, and what does this thing need to reach it." That's why context, tools, and the Agent harness around the model matter as much as the model itself.