alt Hacker NewsThe DevTeam released nethack-3.4.3 in Dec 2003, and then pretty much went dormant for 11 years -- no new releases, no roadmap, nothing. So some time around 2013 some people not connected to the DevTeam created this project: http://nethack4.org/ . So now the DevTeam skips 4.x version numbers completely to avoid confusion.
man that's super shady that they didn't rename the split if they didn't have buy in from the original devs to take over the project.