For those unfamiliar, Knuth's versioning scheme approaches pi and therefore never reaches 4.0 [0]
> In his seminal text layout system, TeX, and his equally brilliant typeface design system, METAFONT, Donald uses a versioning number system that asymptotically approaches perfection. The version numbers of TeX approach π (the current version is 3.14159265) and the version numbers of METAFONT approach e.
You’re leaving out the best part! When he passes (hopefully not anytime soon[a]) the version number of TeX will become pi. Any and all bugs will become “features” at that point. Same with METAFONT; it’ll become e.
[a]: I’d love to get a full and complete set of The Art of Computer Programming (all volumes) written first (on his own time, of course), but I doubt that’ll actually happen. According to Wikipedia, there’s supposed to be 7 volumes, and he’s still working on the second half(?) of the 4th.
> In his seminal text layout system, TeX, and his equally brilliant typeface design system, METAFONT, Donald uses a versioning number system that asymptotically approaches perfection. The version numbers of TeX approach π (the current version is 3.14159265) and the version numbers of METAFONT approach e.
[0] http://sentimentalversioning.org/