If ... if it is a russian minisub (a prototype?) there should be a mother-uboat in international waters. Same applies for other nations.
btw if the russians want SIGINT data, they send their Tu-95 Bombers with SIGINT gear ... as they have done in 2013. why risk a sub or minisub?
my guess its the successor of NR-1 ... lets call it NR-2.
a good book to read about NR-1:
It was impossibly expensive, extraordinarily dangerous, and as a secret weapon, completely unarmed. For the American military, the state-of-the-art submersible, christened NR-1, would be the most closely guarded-and revolutionary-secret of the Cold War. The pet project of Admiral Hyman Rickover, the father of the nuclear Navy, the 400-ton submarine with a miniature nuclear reactor was designed to dive deeper than any other submarine. But such depths also meant the crew would be cut off from all possible rescue should something go wrong. Now, the full story of the NR-1 is told for the first time through eyewitness accounts by the original crew-including co-author Lee Vyborny-who dared go where no men had gone before.
One equal temper of heroic hearts,
Made weak by time and fate, but strong in will
To strive, to seek, to find, and not to yield.