What's new in Android 8 (Oreo)
Before getting into the new features present in Android 8 (Oreo) and its update 8.1, it's worth discussing a few truths about Android updates: phone manufacturers customize Android to such an extent that the features present on a given device may vary greatly from those offered by Android itself: manufacturers often add new features or subtle modify those in Android, in order to differentiate themselves competitively. As a result, your device may have some of these features even without updating to Android 8 (Oreo).
When you upgrade an existing device to a new version of Android, it's possible that not much will look any different. Much of the look and feel of a device is determined by the apps installed on it or the customizations applied by the device manufacturer, whereas new Android features may be hidden under the surface.
When watching a video, Picture-In-Picture mode allows you to switch to using other apps, but keep the video playing in a small box in the corner of the screen, which can be moved around as needed. This allows for "distracted viewing" - when you do not want to direct your complete attention to the video but want to accomplish other tasks while you watch.
This feature is dependent on app support, with native players supporting it. At the time of writing, YouTube only support it for YouTube Red paid subscribers.
When an app can send more than one different type of notification, it can now let you customize the behavior of each of these types of notification in a separate way.
In previous versions of Android, it was possible for the user to have system-wide control over app notifications on a per-app basis, but it was not possible to distinguish between different categories of notification from a single app - when blocking notifications from an app or disabling sound, all notifications from that app were affected. Some apps provided their own settings for managing different types of notifications, with varying levels of customization per app and no system enforcement. With Notification channels, apps can now let users block or allow notifications per type and have a consistent system-wide experience.
Android 8 (Oreo) introduces the ability to snooze notifications, allowing the notification to be hidden for a while, but re-appear later.
While this functionality already existed in some contexts (such as alarms set by the clock app), this new feature standardizes the functionality making it easier to snooze more notifications.
Traditionally, app icons on Android (such as those on the home screen) have not conformed to a uniform shape, such as rounded squares, but can be any shape at all. The original intention of this was to let icons represent real objects better: an icon for a camera could be shaped like an actual camera, and an icon for a clock can be shaped like an actual clock, rather than having a square icon and just having a picture inside that square.
Over time, however, it's become clear that app icons which are plain squares are very common among third party apps, and even in some manufacturer customization layers, leading to an inconsistency on home screens between icons with a square, rounded square or circular background, and icons which have no background and whose shape is determined by the design of the icon itself. What's more, even among those choosing, for example, a rounded square, the size and roundness of the square varies. This leads to a less uniform appearance than, for example, Apple's iOS.
Adaptive icons let app icons change their appearance to conform to a given user-selected style. For example, a user can elect to make all app icons the shape of a "squircle" (a square circle) and the icons themselves will be modified to become this shape. And then the user could decide to make all icons be a "circle", and all app icons will take a circular form.
Apps supporting this new feature now need to provide not just a single version of their app icon, but multiple images, allowing for their shape to be adapted by combining these images. However, for apps who do not provide adaptive icons, Android 8 intelligently modifies the icon itself, by deciding whether it can simply be cropped, or whether it should actually add a background shape to the icon and place the icon inside it. The end result is that all icons will be consistent, with non-adaptive icons being adapted in the best way that an algorithm has decided.
Android 8 (Oreo) introduces a new Autofill framework, making it easier for the operating system to remember frequently used but private information such as login details, credit card details or addresses.
Previously, this type of functionality was available within Google Chrome, and made available via Google to certain other apps (possibly including other browsers), but it wasn't universal; many apps which did not implement these Google interfaces provided no way to access Autofill information.
The new Autofill framework exposes this functionality in new places. Most interestingly for users of third party password managers like LastPass and 1Password, however, is that these alternative password managers can also be used by Android's autofill as an alternative to Google's own system, making these password managers work more reliably on Android 8 and above, once they implement support.
Background execution limits
The new Background execution limits on Android 8 (Oreo) imposes new restrictions on apps that access services or receive messages while running in the background - that is, while the app is not currently visible or being interacted with. Apps wishing to access services or respond to system messages while in the background will now need to do so in new ways which can help the app reduce its impact on performance and battery life.