From the top post in that thread: Most of this work has been on Javascript, which is single-threaded and less mutable than Python, but PyPy has also made some

From the top post in that thread: Most of this work has been on Javascript, which is single-threaded and less mutable than Python, but PyPy has also made some significant contributions. PyPy has a GIL. There is also work on Ruby. Ruby is even more mutable than Python, but also has a GIL. Work on Ruby mirrors that on Javascript.