Urban Terror 4.2 is so radically different from Urban Terror 4.1 that it's not going to even be called "4.2", but rather is being renamed to "Urban Terror HD." While renaming the title to Urban Terror HD isn't a big deal, the big news is the departure from the open-source Quake 3 code-base to now being an official Quake 3 licensee with an official copy of the Quake 3 engine code-base.
From the announcement, "Frozen Sand is going to ship as an official Q3 licensee, forked properly from the 1.32b Quake sources. The GPL stuff we've made public releases of (IoUrbanTerror 4.1 and IOBumpy) will still have their sources available, but there won’t be another Q3/GPL'd Engine Urban Terror release. From the next version on out, Urban Terror will be its own standalone game with its own engine and no longer a mod. This means we can do the tech we want instead of having to keep backwards compatibility with vanilla Q3."
The first beta of Urban Terror HD is expected to arrive before year's end (before Christmas to be exact) while the official release will come likely in 2011. The Urban Terror HD developers have spent more time than anticipated working on this "4.2" release now with all of these fundamental changes and they also now are sorting out some GPL licensing issues with their departure from the open-source code-base.
Urban Terror developers have also been working out an anti-cheat implementation and there is talk that Urban Terror (HD) is no longer even going to be available for free going forward. It's unknown what operating system platforms will continue to be supported by Urban Terror HD.