The Oauth2 API is the primary API and most addresses start with
https://account.y8.com/api/v1/json/ so most of the time it is easy to spot. There are two types of access tokens and a many APIs to choose from. Read below for more details about the Oauth2 API.
Session based API
The session based authentication uses a session key instead of a token. It is mostly used with the Unity3d and Flash interfaces.
The Game API provides application level features like achievements on top of the session based auth. It is based on the open source Playtomic API but is not directly compatible.
The Game Analytics API gives application developers insights into how their game is being distributed and used by end users.
Used in mobile games to promote the network of mobile games.