Agent

In a chat, you ask and the model answers once. With an agent, you describe the goal and it plans, acts, looks at the result and adjusts, over and over, until it is done or needs you.

What turns a model into an agent is the harness: the software that gives the model tools and limits.

When it makes a difference

In multi-step tasks that depend on what is in your files or systems: organizing documents, updating a spreadsheet from emails, changing code. For a one-off question, a chat is enough.