Is there any way to preview freestyle lines using cycles? When using blender render freestyle lines will be previewed in the viewport while in render mode. This doesn't appear to be the case for cycles, but I'm thinking it is just an option somewhere that I have either unchecked or overlooked. If not, are there any addons or alternatives to previewing the lines without having to render every time?
No
As of 2.79, unfortunately there is no way to preview Freestyle lines using Cycles.