Kuznyechik is a 128-bit block cipher first published in 2015 and defined in the National Standard of the Russian Federation GOST R 34.12-2015 and also in RFC 7801. It supersedes the old GOST-89 block cipher although it doesn't obsolete it.
VeraCrypt uses Kuznyechik with 10 rounds and a 256-bit key operating in XTS mode (see the section Modes of Operation).
