All of the APIs documented in the Nintex Workflow 2010 SDK will be supported in Nintex Workflow 2013.
SharePoint 2013 brings with it a new style look and feel. Consequently, Nintex Workflow 2013 has been restyled to match SharePoint 2013. Custom workflow actions developed for NW 2010 may need to be updated to utilise new NW 2013 style elements