Lean has had four versions; it is currently at Lean 4, and it remained at Lean 2 for years.

“He feels like they think that he has more time than he does, and most importantly, he has, like, a vision for where he wants Lean to go. There ultimately are four v- four versions of Lean.”

“We're currently on Lean 4, but for years, you know, we were at Lean 2. And J- uh, Leo saw where he wanted it to go, and he felt inhibited in his ability to actually find the time to do it because he was answering all these essentially, like, user support questions and, uh, queries from mathematicians.”