From Franz-Stefan Gady at The Diplomat:

Russian President Vladimir Putin announced during his annual State of the Nation address on March 1 that the Russian defense industry has begun developing an intercontinental-range nuclear-powered cruise missile capable of penetrating any interceptor-based missile defense system.

“We’ve started the development of new types of strategic weapons that do not use ballistic flight paths on the way to the target. This means that the missile defense systems are useless as a counter-means and just senseless,” Putin said in his speech.

“One of them is creation of a small-size highly powerful nuclear power plant that can be planted inside the hull of a cruise missile identical to our air-launched X-101 or the United States’ Tomahawk, but at the same time is capable of guaranteeing a flight range that is dozens of times greater, which is practically unlimited,” he added…

“A low-flying low-visibility cruise missile armed with a nuclear warhead and possessing a practically unlimited range, unpredictable flight path and the capability to impregnate practically all interception lines is invulnerable to all existing and future anti-missile and air defense weapons,” Putin said.

He also noted that the new nuclear-powered cruise missile was already tested in 2017. “During the flight the power plant achieved the design capacity and thrust. The launch of the missile and the tests on the ground allow for starting work to create a fundamentally new type of weapon — a strategic nuclear missile equipped with a nuclear power plant,” he noted…

During  his 35-minute speech, Putin also revealed the existence of three additional strategic thermonuclear weapons systems including the Status-6 [long-range nuclear torpedo], the Sarmat intercontinental ballistic missile (ICBM), a new hypersonic air-launched cruise missile, and the “Avangard” hypersonic glide vehicle.

From Wikipedia:

The RS-28 Sarmat is a Russian liquid-fueled, MIRV-equipped, super-heavythermonuclear armed intercontinental ballistic missile…

Its large payload of about 10 tonnes would allow for up to 10 heavy warheads or 15 lighter ones or up to 24 hypersonic glide vehicles Yu-71/Yu-74,^[5][6][7] or a combination of warheads and massive amounts of countermeasures designed to defeat anti-missile systems;^[8][9] it was heralded by the Russian military as a response to the U.S. Prompt Global Strike.^[10] It is suspected to have a Fractional Orbital Bombardment (FOBS) capability.^[4]