I read it in the news about five months ago but I can't find the story again.
So, sorry, but I can't provide the source. However, it's obvious that Russia is developing new weapons systems and larger size warhead isn't out of the question with modern missile and rocketry technology.
The ABM treaty and START II no longer exist because the U.S and Russian removals of them, so now is another period of nuclear rearmament. However, now, the countries have no need to test physically because computers can simulate a nuclear explosion, albeit it does take three months to do so. This development as rendered the Comprehensive Test Ban Treaty obselete - and pointless!
The Moscow Treaty, or SORT, is also missing key elements of what is truely needed for nuclear disarmement. While the number of warheads deployed will be reduced, they won't be destroyed - only stored. And the tactical weapons of the two great nations were not mentioned.
Is the Cold War really over?
Anywho, I'll continue looking for the news story.