What is known about Object 1335, a secret cold-war era bunker Russia revived?

Object 1335, a secret Cold War-era underground command complex buried inside mountain in remote Russian village, has been revived. Linked to 'Dead Hand' nuclear command system, it could be used to launch nuclear arsenal if Russia comes under nuclear attack. A joint investigation found it underwent major upgrades between 2018 and 2024. It was believed to be inactive for years.