Google Play Services can be thought of as a backbone inner worked to many of Google's different apps and services on Android devices, and this includes the upcoming mobile payments solution they'll be adding to devices in the near future known as Android Pay. While there has been a number of different Google retail partners stating that they're now set up to accept Android Pay as a form of payment, the app nor the service are ready for primetime. Google is however getting things ready by prepping Google Play Services to work with Android Pay when they're ready to flip the switch and turn things on.
With the latest update to Play Services which should bring users to version 8.1, Google is laying the groundwork for Android Pay to be up and running by adding the necessary bits and pieces into the Play Services apk which started updating for a small number of people last week. Google still hasn't enabled Android Pay yet though and the app hasn't appeared in the Play Store for download, so until the service is activated and the app is installable, you won't be able to use it. Exercising some ADB commands though will allow you to check out what the Android Pay setup experience looks like if you care to know. To initiate this process you'll have to connect your device to your computer through ADB via a microUSB cable, then enter the following command (without the quotes) "adb shell am start -n com.google.android.gms/com.google.android.gms.tapandpay.settings.TapAndPaySettingsActivity" which should run the tap and pay screens. You can also run the command "adb shell am start -n com.google.android.gms/com.google.android.gms.tapandpay.ui.WarmWelcomeActivity" to open up and run the welcome screen of Android Pay.
In addition to the Android Pay framework being included with this version of Play Services, it looks like Google has also added in some more strings relating to "Kids Accounts" which they talked about earlier this year. Kids Accounts don't appear to be quite ready with this version of Play Services, but with addition of new strings it suggests Google is a little bit further along and may be gearing up to soon launch Kids Accounts capabilities in the near future. If you're wanting to download the latest version of Play Services there are three downloads. Both the first and the second download are meant for users on Android 5.0 and 5.1 Lollipop (236 and 238) while the third download is meant for users running the latest version of the Android 6.0 Developer Preview (438). For the first two, the different between 6 and 8 relates to your screen dpi, so to find out which is fit for your device, open up settings, go to apps, open Google Play Services and look at the last three numbers in the parenthesis at the top of the screen. If your number is a 6 then you'd use the download link for 236, if it's an 8 then you'd use the download link for 238, and as stated if you're on Android 6.0 dev preview 3 you'd use the link for 438.