"We think of the breakdown roughly as follows: of our roughly 30% original speedup, 10% is going into Pyston-lite, 10% was done independently by the CPython team between 3.8 and main, and the remaining 10% we are hoping to contribute back upstream."

To compare with Javascript: if I remember, as it appeared, V8 JIT was orders of magnitude faster, compared to the interpreted code.

There was also a bunch of effort being put into efficiency of JavaScript. But now the tables have been changed and Microsoft is putting a large amount of effort into Python .