Things I have heard are they are not necessarily US secrets. Could well be capabilities/readiness of interest to other neighboring / competing nations.
Nations with
US
Russia
UK
France
China
India
Pakistan
North Korea
Undeclared
Israel
from wiki
Israel is widely believed to have been the sixth country in the world to develop nuclear weapons, but it has not acknowledged its nuclear forces. It had "rudimentary, but deliverable," nuclear weapons available as early as 1966.[89][90][91][92][93][94][95][10] Israel is not a party to the NPT. Israel engages in strategic ambiguity, saying it would not be the first country to "introduce" nuclear weapons into the region, but refusing to otherwise confirm or deny a nuclear weapons program or arsenal. This policy of "nuclear opacity" has been interpreted as an attempt to get the benefits of deterrence with a minimal political cost.[10][11] Due to a US ban on funding countries that have weapons of mass destruction, Israel would lose around $2 billion a year in military and other aid from the US if it admitted to possessing nuclear weapons.[7]
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Which brings up issues of our trustworthiness .
For instance, should the capabilities of Israel be the subject, I can right off the top of my head 2 nations that would be very very interested.
Same for Pakistan --- out of that list there are 2 bordering nations that would love having outside info on Pakistani capabilities/ readiness