Approximate marked length spectrum rigidity in coarse geometry

We compare the marked length spectra of isometric actions of groups with non‐positively curved features. Inspired by the recent works of Butt, we study approximate versions of marked length spectrum rigidity. We show that for pairs of metrics, the supremum of the quotient of their marked length spectra is approximately determined by their marked length spectra restricted to an appropriate finite set of conjugacy classes. Applying this to fundamental groups of closed negatively curved Riemannian manifolds allows us to refine Butt's result. Our results, however, apply in greater generality and do not require the acting group to be hyperbolic. For example, we are able to compare the marked length spectra associated to mapping class groups acting on their Cayley graphs or on the curve graph.