Uniqueness conjecture for asymptotic cones of gravitational instantons

Let $(M,g)$ be a gravitational instanton. Asymptotic-cone uniqueness conjecture. The gravitational instanton $(M,g)$ has a unique asymptotic cone. Uniqueness is known for complete Riemannian manifolds with curvature decaying faster than quadratically, while it remains open in the general gravitational-instanton setting.