The Google Calendar API moved to version 3 months ago; however, many developers have continued to hang on to v1 and v2 integrations. In less than a month, on Nov. 17, Google will shut down v1 and v2 in accordance with its Deprecation Policy. Google has published an entire Migration Guide to assist developers' transition, and many third-party solution providers have released packages to further streamline the process.
Before migrating to version 3, Google encourages developers to gain competency with version 3 concepts. The Get Started and API Reference docs will facilitate version 3 familiarity. Google's Migration Guide allows developers to migrate event resources, calendar resources, setting resources and access-control rule resources.
The Google Calendar API, version 3, is based on a new API infrastructure that renders the API incompatible with older versions built on top of Google Data Protocol (GData). Instead of GData, version 3 is JSON based. Additional updates in version 3 include efficient synchronization of resources, push notification support for all calendar collections, custom colors for calendar, and enhanced Google+ events compatibility. To learn more about migration, the v1/v2 shutdown or version 3, visit the Calendar API site.