The SOAP API is continuously undergoing updates and improvements, and is available for use in both a Release version and a Beta version.
The Release version of the SOAP API is stable and is not undergoing changes. Its functionality will be maintained in future versions.
Each Beta release cycle is 6 months, during which time the Beta release is functional and available for use. You can use the Beta version in the same manner as the Release 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 version, and the next version is created as the new Beta version.
Currently, SOAP API v1 is the Release version and, as of 2012-09-01, SOAP API v2 is available to use as the Beta version.