  We review a recollement for derived categories of DG categories arising from
Drinfeld quotients. As an application we show that an exact sequence well-known
in K-theory descends to numerical K-groups provided that either the quotient or
the category we take the quotient with has a Serre functor, and if either the
quotient functor preserves compactness or if the K-group of the quotient is
torsion-free.
