
Vim 9.0 has a lot of small additions while the big change is Vim9 for the Vim script language. Vim9 is focused on better performance so much so that " An increase in execution speed of 10 to 100 times can be expected. " Vim9 script is much faster thanks to compiling commands into instructions for efficient execution. However, there is backwards compatibility breakage in some areas as a result of the Vim9 script changes and trying to make it more efficient.
Vim9 script also works towards avoiding Vim-specific constructions and moving closer to constructs commonly used by the likes of JavaScript, TypeScript, and Java.
More details on the changes to find with Vim 9.0 via Vim.org .