Hypersonic missiles are not a terrifying new weapon. They are just another cog in the terrifying but remarkably stable strategy called nuclear deterrence. "The Avangard hypersonic glide vehicle entered service at 10:00 Moscow time on 27 December," boasted Russian Defense Minister Sergei Shoigu — and nobody quailed in their boots.
The new Russian missile can deliver nuclear weapons, of course, and the Russians are very proud of it. As President Vladimir Putin said, "Not a single (other) country possesses hypersonic weapons, let alone continental-range hypersonic weapons."
A hypersonic missile's warheads launch on a rocket. However, instead of going very high and traveling most of the distance through space in a predictable ballistic trajectory before plunging back down into the atmosphere and striking their target, the hypersonic missile's warheads go low early.