A Guide to Which AI to Use in the Agentic Era

I have written eight of these guides since ChatGPT came out, but this version represents a very large break with the past, because what it means to "use AI" has changed dramatically. Until a few months ago, for the vast majority of people, "using AI" meant talking to a chatbot in a back-and-forth conversation. But over the past few months, it has become practical to use AI as an agent: you can assign them to a task and they do them, using tools as appropriate. Because of this change, you have to consider three things when deciding what AI to use: Models, Apps, and Harnesses.