Russia's original (Project 877) Kilo subs have been operating since 1980.
But the newest sub-class is the Improved Kilo II, Project 636.3. The Improved Kilo II first entered service in 2013 and is being supplied to the Russian Navy only.
The indomitable "Jive Turkey" presents a clear, well-paced, Youtube description of Improved Kilo II Project 636.6 at https://youtu.be/OIpILOFfnYM and below
Highlights of this August 2019 Youtube (usefully seen in conjunction with this list) include:
determined from 1 yard of B-261)