US/UK nuclear warhead developments

Last week the US agency responsible for building & designing nuclear weapons put out “Remarks” with some new information, including:
 
1. Last year, the US modernised/rebuilt 200 nuclear warheads. Next year it intends to spend US$21billion on them (I think that means on new warheads).
 
2. A new warhead design should begin production in the 2030s (the W87-1).
 
In addition, it was noted that (a) China, which historically had a relatively small nuclear arsenal, is catching up with the US, and (b) civil R&D efforts will put more pressure on the non-proliferation regime. For instance, AI & other disruptive technologies could make nuclear weapon design easier for proliferating states, and the further exploration of nuclear alternatives to fossil fuels might stretch global safe-guards
 
Also, a recent article discusses the new UK designed “sovereign” nuclear warhead, to be called Astraea.