What is Russia's Burevestnik Missile?

Meet the Burevestnik: Russia’s nuclear-powered missile with near-unlimited range and unpredictable flight paths. Unlike any conventional missile, it uses a compact nuclear reactor that lets it stay airborne for hours, flying low to evade radar. Russia calls it “invulnerable” to missile defenses, but experts warn of serious risks and there are doubts about its real impact. Is this the new game changer in the nuclear arms race or just a dangerous gamble?