Custom metrics refer to any metrics that are not part of our regular integration suite, for example using custom checks or API-level metrics in your application stack. To clarify, some integrations can potentially emit an unlimited number of metrics that will count as custom, further details can be found here.
Pro plans include 100 custom metrics per host and Enterprise plans include 200 custom metrics per host. This number is averaged across all paid hosts. Additional custom metrics packages can be purchased. Existing customers can contact Customer Success. New customers can contact Sales.