What distinguishes an AI agent from a basic single-turn chat interaction?

A single-turn exchange has one shape: text goes in, text comes out, and the interaction ends the moment the response is produced. An agent does not stop there. It emits a tool call, something outside the model executes that call, the result is appended back into the conversation, and the model decides its next move with that result in hand. Anthropic puts the pattern plainly: agents are typically just LLMs using tools based on environmental feedback in a loop. The Claude API version of it is a round trip, repeated. Because it is a loop, it needs an exit, which is either the goal being met or a stopping condition such as a maximum iteration count.

So autonomy here is not mysterious. It is three mechanics: the model can request an action instead of prose, your code runs it, and the result re-enters context.

The wrong answers each miss one of those. Response length was never the distinction, so a one-sentence cap is irrelevant. Tools are not absent from an agent; they are the mechanism. And a human typing every step describes ordinary chat, the thing an agent replaces.