What each version of the SDK and the checkout brings. The log is kept in Spanish.
The widget update log is kept in Spanish: Novedades del widget. Each entry says whether the change is in the SDK (it reaches you when you upgrade) or in the widget (it reaches you on its own), and whether you have to do anything.
The latest version is 1.7.0. To integrate the checkout, see Checkout widget. For API changes, see API updates.