Note: The original post was written before the official announcement. It remains here unmodified as a historical reference. For updated information, see the bottom of the post.

It is expected that Google will reveal Play Games at Google I/O in two days. What is Play Games? It's Google's new service for Android that adds achievements, leaderboards, cloud saves, and more. It hasn't been announced and can't be used yet. But there's still a fair bit known about it. Let's take a look.

Play Games will be implemented through Google Play services. There are two components to Google Play services: the Google Play services APK and the client library. The APK is automatically installed and updated by Google Play. The client library is included with apps that interact with Play Services. Play Games will require updated versions of both.

The updated Play services client library first showed up in the MyGlass app. Here's what Android Police found inside.

These classes would be used for real-time multiplayer and turn-based multiplayer.

Also supported are leaderboards, invitations, and lobbies.

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With all this other stuff, it would be a shame if Google forgot about achievements. Fortunately, they didn't. Look, right there!

Filenames are boring. What else is there? What about the update to the Google Play APK? Here's what Android Police found.

The Play Games icon looks like the Games icon used in the new version of the Play Store, with the standard Google Play pattern applied to it.

Activities for achievement lists, leaderboards, invitations, and more are included. It is unclear whether developers will be able to implement their own custom UIs for these functions or whether these prebuilt activities must be used.

Play Games accounts are Google+ accounts, so your real name will probably be visible to everyone you play with. In the Play Games settings you have the ability to control which of your Google+ circles can send you notifications. You can also mute games, which I suppose is a way to prevent certain games from sending you notifications.

Leaderboards show the top ranking players of all time, weekly, and today, and you can see how you rank against your friends.

Games can synchronize save data through the user's Google account, keeping your saves up to date on multiple devices.

This is the "achievement unlocked" thingy. I don't know whether there will be a sound when it pops up, so feel free to speculate.Look for more information on May 15, when Google Play Games is expected to be announced.

UPDATE: Google Play game services has been announced at the Google I/O 2013 keynote. Polygon reports that it will also be available for iOS and web.

.. .. That controller looks sure looks like a console one.. When 95% of those games are touch..

But alright. Cool! I'm sure they'll integrate Babel in 2 years. And then Samsung will have Their play-store, with Samsung Achievements on Tizen.

Weird times are ahead.. What with Jony Ive to continue revamping everything he could touch with a friendly-whip.

All this is going to do is further segregate the multiplayer communities on mobile devices. Cross platform play between iOS and Android seems fairly trivial to implement as long as the iOS version doesn't use GameCentre. Now you've got a similar service on Android, further complicating things.

But how else would you represent games? Android does support controllers, so at least it makes more sense than a bound book for Play Books or a filmstrip for Play Movies.

There is a sync adapter for app data and a separate sync adapter for game data. The game data sync adapter appears to be for leaderboards, achievements, etc. The app data sync adapter is more generic, for syncing data from any kind of app. Finally. The existing backup mechanism only handles backup and restore, not synchronization.

The internal code name for Play Games is "OneUp".

Ha, I'd forgotten that Samsung controller existed. Still, hardly going to become a standard. I occasionally plug a Logitech Rumblepad into my Android phone, but support is pretty fleeting and it's only really useful for playing emulators and such.

A unified system is a long time coming to be honest. While Gamecentre was very quickly banished into the "Useless" folder on my iOS homescreen, it's at least better than signing up for a bunch of different services and struggling to remember which ones are which.

Google Play game services has been announced. World of Goo supports it.

Polygon is reporting that it's available for iOS as well, though real-time matchmaking is Android exclusive "for now".

Huh. Wasn't expecting that. Apple usually make it a pain to get apps on the store that compete with their own apps. Remember how long it took Amazon to get the Amazon Music app approved.

In that case, this might make the segregation in the mobile space less common.

More information about Google Play game services has been revealed in the New Developments in Mobile Gaming session, and the developer documentation is up.

There are three achievement states: hidden, revealed, and unlocked. Hidden achievements are basically secret achievements. The existence of the achievement isn't hidden, but its description and icon is. Interestingly, hidden achievements can be revealed without unlocking them.

Games must have at least five achievements. Achievements have point values, but these points aren't exposed to the player so I don't understand the point.

Achievement notifications can be hidden on iOS, which is useful for games that also implement Game Center achievements.

There is a standard achievement list UI, but it is possible for games to implement their own.

Cloud saves keep your saves synchronized across devices, even across operating systems. If you have an Android phone and an iPad, saves will be kept in sync across both devices. That's awesome.

The anti-piracy feature (Android only) will cause game services to fail if none of the Google accounts on the device have purchased the game from the Play Store. This is optional and will only be enabled if the developer manually enables it.