  The notion of d-critical loci was introduced by Joyce in order to give
classical shadows of $(-1)$-shifted symplectic derived schemes. In this paper,
we discuss birational geometry for d-critical loci, by introducing notions such
as `d-critical flips', `d-critical flops', etc. They are not birational maps of
the underlying spaces, but rather should be understood as virtual birational
maps. We show that several wall-crossing phenomena of moduli spaces of stable
objects on Calabi-Yau 3-folds are described in terms of d-critical birational
geometry. Among them, we show that wall-crossing diagrams of
Pandharipande-Thomas (PT) stable pair moduli spaces, which are relevant in
showing the rationality of PT generating series, form a d-critical minimal
model program.
