A Simple Glossary for AI Models, Harnesses, Agents, and Frontier Models

I have been getting lost in AI definitions lately, so here is a simple glossary that may help.

AI model

The large language model that handles the basic completion. You send it text, and it responds with text.

The environment and tools built around the model. A harness may give the model access to web search, MCP servers, or a terminal.

The part responsible for deciding how to use the model and harness to complete tasks that require reasoning and action.

One of the most advanced AI models available at a particular point in time. The label moves as new models arrive.

Originally posted on LinkedIn.