Today's Super Smash Bros. update is all about shared stages between the Wii U and 3DS versions. For the most part, each build has its own exclusive set of stages, but some will be shared. Along with a picture of Wily's Castle on 3DS, director Masahiro Sakurai posted that shared stages may offer slight differences:
This brings us up to 15 exclusive stages per game plus four shared between the two. On reddit, Scotsman333 posted an image macro of all the stages revealed thus far and where they have been placed. More stages are definitely on the way — I doubt each version is only going to have one classic returning stage each, right?
Super Smash Bros. for Nintendo 3DS comes out October 3, while the Wii U build comes out later in winter.