You can get it if you carefully adjust the window width! Or there’s one example in the author’s post – the word “implementation” is hyphenated for me [1].
So it looks like the algorithm tries to minimize hyphenation, which makes sense to be honest.
[1]: https://matklad.github.io/2026/02/14/justifying-text-wrap-pr...
Ha. Oh wow. OK, I got "implementation" to hyphenate... but only once I changed the zoom level, and only for one specific exact window width. One pixel narrower or wider, and it stopped hyphenating.
So hyphenation exists in theory, but I'm just going to go ahead and say that however it's tuned seems completely broken.