In my opinion there are 2 levels, human writes the code with AI assist or AI writes the code with human assist; centuar or reverse-centuar. But this article tries to focus on the evolution of the ideas and mistakenly terms them as levels (indicating a skill ladder as other commenters have noted) when they are more like stages that the AI ecosystem has evolved through. The article reads better if you think of it that way.

There is another level - AI writes the code with AI assist.