  We investigate a model that modifies general relativity on cosmological
scales, specifically by having a `glitch' in the gravitational constant between
the cosmological (super-horizon) and Newtonian (sub-horizon) regimes, as
motivated e.g. in the Ho\v{r}ava-Lifshitz proposal or in the Einstein-aether
framework. This gives a single-parameter extension to the standard $\Lambda$CDM
model, which is equivalent to adding a dark energy component, but where the
energy density of this component can have either sign. Fitting to data from the
Planck satellite, we find that negative contributions are, in fact, preferred.
Additionally, we find that roughly one percent weaker superhorizon gravity can
somewhat ease the Hubble and clustering tensions in a range of cosmological
observations, although at the expense of spoiling fits to the baryonic acoustic
oscillation scale in galaxy surveys. Therefore, the extra parametric freedom
offered by our model deserves further exploration, and we discuss how future
observations may elucidate this potential cosmic glitch in gravity, through a
four-fold reduction in statistical uncertainties.
