Norway has not yet given further details about which submarines, but the "rumors" say Borei Class.

Borei class includes a compact and integrated hydrodynamically efficient hull for reduced broadband noise and the first ever use of pump-jet propulsion on a Russian nuclear submarine.

Russian news service TASS claimed the noise level is to be five times lower when compared to the third-generation nuclear-powered Akula-class submarines and two times lower than that of the U.S. Virginia-class submarines. The acoustic signature of Borei is significantly stealthier than that of the previous generations of Russian SSBNs, but it has been reported that their hydraulic pumps become noisier after a relatively short period of operation, reducing the stealth capabilities of the submarine.

The Borei submarines are approximately 170 meters (560 ft) long, 13 meters (43 ft) in diameter, and have a maximum submerged speed of at least 46 kilometers per hour (25 kn; 29 mph). They are equipped with a floating rescue chamber designed to fit in the whole crew. 

Smaller than the Typhoon class, the Boreis were initially reported to carry 12 missiles but are able to carry four more due to the decrease in mass of the 36-ton Bulava SLBM (a modified version of the Topol-M ICBM) over the originally proposed R-39UTTH Bark. Cost was estimated in 2010 at some ?23 billion (USD$734 million, equivalent to US$863 million in 2020 terms.  In comparison the cost of an Ohio-class SSBN was around US$2 billion per boat (1997 prices, equivalent to over US$3 billion in 2020 terms.