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As the term "agent" gains clarity in AI discourse, experts agree on a succinct definition: an LLM agent runs tools iteratively to meet objectives, streamlining communication and advancing practical applications.
In recent weeks, I've noticed a significant shift in how the term "agent" is used within AI conversations. Specifically, it's now being used more consistently and without the need for lengthy definitions or disclaimers. This marks a crucial turning point, as clear terminology is essential for effective communication in any technical field.
For clarity, let’s define what we mean by an "LLM agent":
An LLM agent runs tools in a loop to achieve a goal.
This definition has gained traction and is now widely accepted in the AI engineering community. Here's a breakdown of what this means:
For years, the term "agent" was plagued by ambiguity. Everyone seemed to have a different interpretation, making it difficult to have productive discussions. This problem isn't new; in 1994, Michael Wooldridge noted in Intelligent Agents: Theory and Practice:
Carl Hewitt recently remarked that the question “what is an agent?” is embarrassing for the agent-based computing community in just the same way that the question “what is intelligence?” is embarrassing for the mainstream AI community. The problem is that although the term is widely used, by many people working in closely related areas, it defies attempts to produce a single universally accepted definition.
The lack of a shared definition can lead to confusion and miscommunication. However, with the current consensus, we can now have more meaningful and productive conversations about LLM agents.

To illustrate how this works, let’s consider an example:
Implementing an LLM agent involves several key components:
While specific benchmarks for LLM agents are still evolving, early results show promising performance in task completion rates and efficiency. For instance, Anthropic’s research has demonstrated that their agents can achieve high success rates in complex tasks like automated customer support and data analysis.
The widespread acceptance of the "tools in a loop to achieve a goal" definition for LLM agents is a significant step forward. It provides a clear and practical framework for discussing and developing these systems, enabling more effective collaboration and innovation in the AI community.
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↗ https://simonwillison.net/2025/Sep/18/agents/?utm_source=tldrai
About the author
Kai built ML infrastructure at a Bay Area startup before developing an obsession with transformer architectures and inference optimisation that eventually pulled him out of product work entirely. A stint at a compute research lab sharpened his instinct for what actually matters in a model release versus what is marketing. He writes from the inside — from the perspective of someone who has debugged the systems he is describing at three in the morning. He is allergic to hype and instinctively drawn to the unglamorous plumbing questions that everyone else skips over.
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19 September 2025
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