Is there and endpoint for Sentry usage stats? Currently, we need to go to Sentry UI Stats page every time.

Sentry doesn't have a documented API for usage details on the Stats page.

However, there are some endpoints that can be useful to retrieve the similar information. Please see the Retrieve an Organization's Events Count by Project and List a Project's Error Events endpoints.

There is an existing feature request on GitHub to support Aggregated Error Reports via API.