K-stability of Fano 3-folds in the World of Null-A

A variety is said to satisfy Condition (A) ( A ) if every finite abelian subgroup of its automorphism group has a fixed point. We show that a smooth Fano 3-fold not satisfying Condition (A) ( A ) is K-polystable unless it is contained in eight exceptional deformation families (seven of them consist of one smooth member, and one of them has two-parameter moduli).