When NASA spent millions to develop a ballpoint that would write in space, Russia solved the problem with a lead pencil. They have applied the same low-tech solution to the problem of how to defend Russia against the threat of conventionally armed hypersonic missiles that can strike at 5+ times the speed of sound...
Better radar? Missile shields? Supercomputers? Laser interceptors? Nope.
Just let your enemy know that if they use them, irrespective of what warhead they put on them, you will reply with NUKES.
This is the Future of War