pdfTeX was an extension to TeX (as was XeTeX), for a long time maintained as a collection of change-files applied to the canonical TeX source, although nowadays

pdfTeX was an extension to TeX (as was XeTeX), for a long time maintained as a collection of change-files applied to the canonical TeX source, although nowadays they're managed as separate WEB files. LuaTeX was in turn an extension of pdfTeX, but I think at this point it would be better described as a fork rather than an extension. (Though it's not clear to me exactly how to distinguish these concepts.) Anyhow, I believe the 3.141592653 updates have already been ported to all these engines.