The SOAP API is continuously undergoing updates and improvements, and is available for use in both a Release Stable version and a Beta Development version.
The Release Stable version of the SOAP API is stable fully functional and is not undergoing changes. Its functionality will be maintained in future versions.
Each Beta Development release cycle is 6 months, during which time the Beta Development release is functional and available for use but is undergoing changes and may not stable. You can use the Beta Development version in the same manner as the Release Stable version, except that the wsdl is different and you must modify your application as needed to accommodate our changes to the API. After the 6-month cycle, the SOAP API becomes the new Release Stable version, and the next version is created as the new Beta Development version.
Currently, SOAP API v1 is the Release version and, as of 2012-09-01, Stable version. The SOAP API v2 is will soon be available to use as the Beta versionDevelopment version.