[jsn]

The 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.

[Suppafly]

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.

[chongli]

The people who worked on NetHack4 are now members of the mainline DevTeam and were heavily involved in the 5.0 release.