K-329 Belgorod is a modified design of the Oscar II class Russian nuclear submarine. It was laid down in July 1992 as a Project 949A cruise missile submarine, NATO designation Oscar II class. It was redesigned and the partly built hull was reconfigured as a special operations vessel, able to operate unmanned underwater vehicles. The vessel was relaid in December 2012. Due to chronic underfunding, its construction was suspended, then resumed at a low rate of progress before the ship was redesigned to become a unique vessel — the first Russian fifth-generation submarine, according to the Ministry of Defence.

The Oscar class, Soviet designations Project 949 Granit and Project 949A Antey, are a series of nuclear-powered cruise missile submarines designed in the Soviet Union for the Soviet Navy. First built in the 1970s, six remain in service with the Russian Navy. Two other vessels were slated to be modernized since at least 2017 as Project 949AM, to extend their service life and increase combat capabilities but it is unclear whether work continues as of 2023.