Russia has hypersonic reentry vehicles, they are pretty much impossible to intercept (https://en.m.wikipedia.org/wiki/RS-28_Sarmat), each of these MIRV contains 10-15 nuclear warheads or an unspecified number of hypersonic glide vehicles (https://en.m.wikipedia.org/wiki/Avangard_(hypersonic_glide_v... )with nuclear payloads. They figured out the hydrodynamics to make the hypersonic glide vehicles work, I believe the US is roughly a decade behind on that. Note that this requires genuinely hard math to do and the US funding on this was temporarily suspended because it was thought to be infeasible.