How Russia's new Hypersonic missile works :
The missile doesn't have any propulsion or engine. Rather it's first launched with an ICBM which carries it to a very high altitude.
Then launched. It rides the shockwave created, surfing the wave like a surfer, that pushes it into hypersonic speed.
USA had been trying to build such missiles, but its two tests failed. While Russia has already ran a successful test, and now claims ready for deployment.
USA doesn't have any defense against hypersonic missiles.
Note : Hypersonic speed is Mach 20. Though anything above 5 is called hypersonic.