Fly now includes built-in Prometheus metrics for all its apps, allowing users to monitor performance, create alerts, and export their own custom metrics. The platform uses a Prometheus-style system with three types of metrics: counters, gauges, and histograms. Users can query these metrics using the PromQL language and visualize them in Grafana. Fly also supports custom metric generation for applications built on various frameworks such as Go, Python Flask, and Node.js.