We show that for a K–unstable Fano variety, any divisorial valuation computing its
stability threshold induces a nontrivial special test configuration preserving the
stability threshold. When such a divisorial valuation exists, we show that the Fano
variety degenerates to a uniquely determined twisted K–polystable Fano variety. We
also show that the stability threshold can be approximated by divisorial valuations
induced by special test configurations. As an application of the above results and the
analytic work of Datar, Székelyhidi and Ross, we deduce that greatest Ricci lower
bounds of Fano manifolds of fixed dimension form a finite set of rational
numbers. As a key step in the proofs, we adapt the process of Li and Xu
producing special test configurations to twisted K–stability in the sense of
Dervan.
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