  I review recent work on computing radiative corrections to non-abelian gauge
couplings in four-dimensional heterotic vacua with spontaneously broken
supersymmetry. The prototype models can be considered as K3 surfaces with
additional Scherk-Schwarz fluxes inducing the spontaneous $\mathcal{N}=2 \to
\mathcal{N}=0$ breaking. Remarkably, although the gauge thresholds are no
longer BPS protected and receive contributions also from the excitations of the
RNS sector, their difference is still exactly computable and universal. Based
on a talk presented at the DISCRETE 2014 conference at King's College London.
