I believe all CBU should have an 1/8 gap that is filled with mortar. Some manufacturers require joints to be taped with a mesh tape.
I saw someone saying you should have gaps between your pieces of cement board when using it for a tile backer. Is this true? If so how big should the gaps be? Also will the gap be the same size if its a cement board to drywall seam?
I found this on Durocks website "Fit ends and edges of panels closely but not forced together."