api gateway versus service mesh: when to pick one over the other?

hey everyone, ive been thinking a lot about how we manage communication between our microservices. weve used an api gateway for external traffic management for a while, but with our internal service-to-service communication growing, im considering a service mesh. what are your thoughts on the trade-offs? when do you find an api gateway sufficient, and when does a service mesh become a necessity? looking forward to hearing your experiences