One of the reasons Android has become the most popular computer operating system in the world can also create a big headache — any company can do almost anything they want to do with it. That not only means that devices running Android can look very different and use very different hardware, but even "traditional" uses of Android like phones that include support for Google services aren't all going to be running the same version.
There are about 20,000 different devices running Android and most of them are running an older version.
This will never change. Google has tools that make it easier for hardware manufacturers to all migrate to the current version of Android (9 at the time of this writing) but even those tools aren't going to be enough to get every supported device on the same platform version at the same time. Google handles this issue for phones and other devices that follow the Android Compatibility Definitions with some tools like Google Play Services to provide supplemental security improvements and functionality. If you have the Play Store on your phone, you have Google Play Services up and running regardless of the version of Android you're using.
Google also has tools for app developers who want to make use of the cool new things each platform update brings and have their apps be compatible with as many phones as possible. These are known as the Android Support Libraries, and developers can use them to add some of the things that Pie brings to the table back to Oreo or Nougat.
Along with Android 9, one of the big announcements at Google I/O 2018 was Android Jetpack. Jetpack is a set of components for developers that makes it easier to build apps and is comprised of the new AndroidX libraries. One of the features of AndroidX and Jetpack is to make features from the latest versions of Android work on older platform versions. Another great feature is Jetpack's modularity which means it can be updated quickly and independently of Android itself. This makes adding features that work across multiple platform versions much easier.
Right now there aren't a lot of visible features of Pie that can be used in older versions like Oreo and Nougat, but the Support Libraries are filled with changes that help developers build apps for Android Pie that will still function on older versions. That's the most important part, but everyone at Google is excited about how Jetpack and AndroidX will be able to keep bringing newer features to older versions of Android, and I expect we'll see the list grow.
Slices
A Slice is a tiny piece of an app that can be filled with dynamic content and appear anywhere in any Android app or inside any Google-provided service. A Slice can bring important and contextual information from an app right where we need to see it and can include things like live data, intents, inline Actions as well as deep linking to other portions of its parent. Useful information or controls that we want to have at our fingertips without opening an app, like music player controls or flight schedules can appear where we can easily use them.
Slices are something developers can work on right now and will be rolling out to user accounts "soon" — and thanks to Jetpack and the Support Libraries, that means they won't be restricted to only Android 9.
Actions
Google Assistant already brings Conversational Actions to phones with Google Assistant and devices like Google Home and Smart Displays. They're part of your Google account and developers have been eagerly adding more and more of them that you can include in your own routine.
Soon, we'll also have Actions on our phones that use the same ideas. They are designed to bring functionality from an app into any Google service, but what's really cool about them is that Google's AI will bring them automatically and intelligently where you need them when you need them. App Actions are difficult to describe, but when you see one in action it just clicks; you can see how App Actions will work right now. Visit Google.com and type something like " how many U.S. dollars is 25 Euros" and you'll be presented with the answer and a small conversion tool you can use right at the top of the page.
While a currency converter isn't that exciting, think of how other apps can inject parts of themselves into things like Search or Gmail or Docs. App Actions are in beta right now, and we expect them to come to our phones soon. Again, thanks to Jetpack and the Android Support Libraries they won't be restricted to Android 9 and almost all of us can use them as they appear.
Google says that any new Android app should work on 90% of active devices. That means it also needs to provide tools and means for apps that feature new APIs and interface elements to work on older versions. We'll keep updating this list as more news about the Android Support Libraries comes to light and look forward to lots of new additions during the 2018 Android Dev Summit in November.
