The most recent update to the SDK is compatible with SI5.5 and continues to be supported by the team here. There have been no major updates to the SDK since our last posted update. You can find information and a link to download here:
SI5 SDK Update 1
Information on our our various support options can be found here:
D-Tools - SDK Features Benefits
Support through the forums is free to all SDK developers.
Best,
The D-Tools Team