  We introduce the fastest known exact algorithm~for~the multiterminal cut
problem with k terminals. In particular, we engineer existing as well as new
data reduction rules. We use the rules within a branch-and-reduce framework and
to boost the performance of an ILP formulation. Our algorithms achieve
improvements in running time of up to multiple orders of magnitudes over the
ILP formulation without data reductions, which has been the de facto standard
used by practitioners. This allows us to solve instances to optimality that are
significantly larger than was previously possible.
