Apple's MetricKit was introduced with iOS 13, offering a simple API for power and performance metrics. In iOS 14, three new trackable metrics were added: CPU instructions, animation hitches, and exit reasons. The exit reasons metric is the most interesting, as it tracks various ways an app can be terminated while running in either the foreground or background. This metric provides a solution to building complex crash reporting pipelines with data from a first-party framework without relying on third-party SDKs or Xcode's limited organizer. However, there are limitations, such as requiring user opt-in for diagnostics & usage data sharing and requesting data only once per day. These limitations may curb adoption, but Apple can address them in future versions of MetricKit.