Comment by bhaak

The story is a bit more convoluted. After the 3.4.3 release in 2003, the DevTeam stopped releasing new versions. They were still responsive when contacted by e-mail, though. But then we also didn't know how the development version looked like.

In 2014 the dev version was leaked to the community and in the following discussions with the DevTeam on how to handle this, the DevTeam got the first shoot of new devs in a while which lead to the release of 3.6.0 in 2015. This version was a polished version of the dev version, also incorporating some of the popular community patches at the time. The 3.6 branch received regular bugfix and security updates (3.6.7 was released in 2023).

Since 3.6.0 there's a mirror repository of NetHack on GitHub. So the development version that was internally numbered 3.7.0 which would become 5.0.0 was always accessible and, contrary to the 3.4.3 era, could be played anytime and was also installed on the public servers to play.