Download the 3.4.d SDK, there are no changes to the sdk between 3.4.d svn revision 25020 and 3.4.e svn revision 26676.3.4.e was labeled preview release, it just adds activiti support, everything else is more or less the same. So if you do not want to try activiti, use 3.4.d if you want the sdk to match.
I've fixed the release document -> https://wiki.alfresco.com/wiki/Alfresco_Community_3.4.e_Download
3.4.e is the community version. There's no such thing as Enterprise 3.4.e; the current enterprise version is Enterprise 3.4.5.There will be a corresponding SDK for the enterprise version. Download from (Alfresco Network) support.alfresco.com. Or if you are using the enterprise trial you can download the SDK from the same URL as you downloaded the rest of alfresco e.g. http://www.alfresco.com/products/ecm/enttrial/?product_module=DM
No there will never be an Enterprise 3.4.X with Activiti. Activiti will be supported in Alfresco Enterprise 4.0.X
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