api gateway vs service mesh when to choose which

hey folks, ive been thinking a lot about how to manage interservice communication in microservice architectures. weve used an api gateway for external traffic routing and some basic auth, but im seeing more and more about service meshes like Istio or Linkerd. it seems like theres overlap, but also distinct use cases. when have you found one to be clearly superior to the other? are there scenarios where youd use both, or is it usually an eitheror decision?