Looking at the code frequency, it looks like development of Lean 3 all but stopped around January 2018. The Lean 4 repo shows lots of activity since January 201

Looking at the code frequency, it looks like development of Lean 3 all but stopped around January 2018. The Lean 4 repo shows lots of activity since January 2019, but isn't in a useable form. What are the future plans for the project? How will this be distributed in a form that mathematicians can use and contribute to?