The perfectoid approach to purity questions

Purity in arithmetic algebraic geometry is the phenomenon of certain invariants of algebraic varieties being insensitive to removing closed subvarieties of sufficiently large codimension, the Hartogs' extension principle being the basic example. The most delicate case of such results is in mixed characteristic (0, p), in which a new approach based on perfectoid rings has recently been introduced. I will overview it and discuss the results that it has yielded so far.