How do Live Activities (ActivityKit) and WeatherKit work, and what are their limits?

Live Activities show real-time, glanceable information (a delivery, a sports score, a ride) on the Lock Screen, in the Dynamic Island and in StandBy. You define an ActivityAttributes type (fixed data, such as the order id) with a nested ContentState (the data that changes), request an activity with Activity.request(attributes:content:pushType:) from the foreground app, and render it in a widget extension with SwiftUI (ActivityConfiguration, with compact, expanded and minimal Dynamic Island layouts). The ContentState is encoded as JSON and must stay small (the combined static attributes and state are limited to 4 KB). Update from the app with activity.update(_:), or, since the app is usually not running, via ActivityKit push notifications: ask for a pushType: .token, send the activity’s push token to your server, and send APNs pushes with apns-push-type: liveactivity and the apns-topic ending in .push-type.liveactivity, carrying a new content-state (with an event of update or end, and optional stale-date). Limits: an activity runs for at most 8 hours of active life (then the system ends it, and it may remain on the Lock Screen up to 4 more hours), there is a cap on concurrent activities per app, updates are budgeted (frequent updates need the NSSupportsLiveActivitiesFrequentUpdates key and may still be throttled), no network from the widget extension (all data comes through the state), and the user can disable them per app. Design for a clear lifecycle: start on an explicit user action or event, update only when something meaningful changes, end promptly with a final state, and handle the user dismissing it. Alerts (AlertConfiguration) can wake the screen for urgent changes.

WeatherKit gives current conditions, hourly and daily forecasts, minute-by-minute precipitation, severe-weather alerts and historical data for a location, through WeatherService.shared.weather(for: location) (or the REST API for non-Apple clients). It needs the WeatherKit capability (an entitlement and an App ID with the service enabled), is metered (a monthly free allowance with Apple Developer Program membership, then paid tiers), returns data as Swift types (Weather, CurrentWeather, HourWeather, DayWeather) with Measurement values that you format for the user’s locale, and requires attribution: show the Apple Weather trademark and a link to the legal source page (WeatherService.shared.attribution) near the data. Cache the results (forecasts change slowly, and caching saves quota and battery), handle the network and entitlement errors, and combine with Core Location for the user’s place (when the user shares it). For both frameworks, check the current limits in the documentation, since quotas and policies evolve.