The startup has been fine tuning the new version -- "APIv2" as Foursquare calls it -- for more than a year with a particular focus on speed, consistency and clarity.
Foursquare has dropped support for XML to make its server more responsive, updated to OAuth2 to make it easier and more secure for users connecting to Foursquare through third-party services, and added much-requested new endpoints for fetching user badges, venue histories, and venue popularity.
Here's how Foursquare describes the new API to developers: "The foursquare APIv2 gives you access to all of the data used by the Foursquare mobile applications, and, in some cases, even more. Integrate checking in or viewing checkins into your application, build tools to help users use or visualize their own history, experiment with new ways of displaying badges, leverage our uniquely rich information about venues or do things we haven't even thought of yet."
If you want to see the new API in action, look no further than the new Foursquare for Android application released a few days ago; it's said to be the first Foursquare client built entirely off of the new API. The application supports a more streamlined approach to checkins and is deeply integrated with the Android operating system.