There are a couple recent changes to the way you build your Android apps with Google Play services (and Firebase SDKs, which are distributed as part of Play services). Here's what you need to know to stay up to date.

1. Play services (and Firebase) dependencies are now available via maven.google.com

Until recently, developers were required to update their Android tools to make use of new versions of the local maven repository that contains Play services compile dependencies. Only after updating were the Android build tools able to locate them. Now, the dependencies are available directly from maven.google.com. You can update your app's Gradle build scripts to use this repository by simply configuring the build like this:

allprojects {
    repositories {
        jcenter()
        maven { url 'https://maven.google.com' }
    }
}

Note the new Google maven repository. This is where dependencies are now hosted. Using Gradle 4.0 and later, you can simply specify google() as a shortcut instead. Once configured like this, Gradle will be able to locate, download, and cache the correct Play services dependencies without requiring an update to the Android build tools. Play services SDKs going back to version 3.1.36 will be available in this repo.

You can read more about Google's maven repo here.

2. Starting with Play services dependencies version 11.2.0, your app's compileSdkVersion must be at least 26

When you upgrade your app's Play services dependencies to 11.2.0 or later, your app's build.gradle must also be updated to specify a compileSdkVersion of at least 26 (Android O). This will not change the way your app runs. You will not be required to update targetSdkVersion. If you do update compileSdkVersion to 26, you may receive an error in your build with the following message referring to the Android support library:

This support library should should not use a different version (25) than the compileSdkVersion (26).

This error can be resolved by upgrading your support library dependencies to at least version 26.0.0. Generally speaking, the compileSdkVersion of your app should always match the major version number of your Android support library dependencies. In this case, you'll need to make them both 26.