After the release of NetHack 3.4.3 in 2003, the NetHack DevTeam went on a long hiatus. 3.4.3 was long considered by some to be the final version of NetHack until December 7, 2015, twelve years after this version's release, when NetHack 3.6.0 was released.
Leaked 3.5.0 source code
In September 2014, a leaked source code distribution described as "NetHack 3.5.0 Beta" was circulated on the Internet, e.g. in the Usenet newsgroup rec.games.roguelike.nethack. In response, the DevTeam posted an official announcement on nethack.org confirming the leak, but refuting any claims that it would represent an official release (beta or otherwise), and also retiring the version numbers 3.4.4 and 3.5, which had been incorrectly associated with the leaked code:
Recently a NetHack source distribution has appeared, claiming to be NetHack 3.5 or 3.5.0 or 3.4.4.
This claim is partially correct. This is our code. However it was not released by us or with our authorization. This code is not ready for release: it is unfinished, unpolished, and almost certainly very buggy. It has not been play-tested for balance or functionality. It is best considered a partial and unfinished rough draft. We will not be supporting this code, nor will we be releasing binaries or bugfixes for it. It will not be available through our website.Due to this incident and to prevent confusion, we will not now nor in the future release anything with a version number of 3.4.4, 3.5, or 3.5.0.
Discussion about this leaked code can be found in the article leaked development version.
NetHack 4 confusion
There is a variant of NetHack 3.4.3 known as NetHack 4, which is not an official version 4 of NetHack from the DevTeam. More confusingly, Ais523, the maintainer of NetHack4, is now on the DevTeam but works on NetHack4 and vanilla separately.
Unlike most other variants, NetHack4 has a drastically different codebase from vanilla, and the DevTeam internally refers to it as NetHack4, with no space. It is not actually version 4 of NetHack, and no such version currently exists.
- Bugs in NetHack 3.6.0 — What will be fixed in the next version