ModelRefs / AI Agent — AI Glossary
AI Agent — AI Glossary
An LLM-driven system that perceives state, plans actions, uses tools, and executes steps toward a goal with minimal human intervention.
Overview
Agents combine reasoning (the LLM), tools (functions/APIs), memory (state), and a control loop. They range from simple single-turn function-callers to multi-step planners orchestrating sub-agents. The key distinction from a chain: an agent chooses its next action dynamically.
Reference details
| Topic | agents |
|---|---|
| Also known as | AI Agent, LLM agent, autonomous agent |
| Last reviewed | 2026-06-24 |
Related terms
Example: A chain vs. an agent, on the same task
Task: “What did we bill Acme last quarter, and is that above their contract cap?” A chain runs fixed steps: query invoices → sum → compare → answer. If the invoice table is empty it returns £0 and stops. An agent decides its next step from what it sees: the empty result prompts it to check whether Acme is billed under a parent account, re-query, then compare. Same tools, same model — the difference is who chooses step two.
Commonly confused with
Not every LLM app that calls a tool is an agent. A single function call inside a fixed pipeline is tool use in a chain. The distinguishing property is control: an agent selects its next action at runtime, so its execution path is not knowable in advance.
When to use it
Reach for it when:
- The number of steps depends on what earlier steps return
- The task needs recovery from partial or failed results
- You can define a stopping condition and a step budget
Reach for something else when:
- The steps are fixed — a chain is cheaper, faster and far easier to test
- Every action is irreversible and unattended, with no human review
- You cannot bound cost: a loop that picks its own next step can pick badly many times
Referenced by
This term is used by the following ModelRefs references:
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Frequently asked questions
What is AI Agent?
An LLM-driven system that perceives state, plans actions, uses tools, and executes steps toward a goal with minimal human intervention.
Is AI Agent the same as AI Agent?
Yes — AI Agent, LLM agent, autonomous agent are common aliases for AI Agent.
What concepts are related to AI Agent?
Closely related concepts include function calling, tool use, agent workflow, mcp.