Hi,

In a new K2 Five installation, there are no thick client designers by default. K2 Studio and K2 for Visual Studio only exist in environments upgraded from early versions to K2 Five. If your environment has recently upgraded to K2 Five, then the thick client tools can be still run in Legacy mode.

There is a new feature, Workflow Rest API to interact with workflow. Is this what you are looking for?

Workflow REST API

http://help.k2.com/onlinehelp/k2five/DevRef/5.0/default.htm#Whats-New.htm