This MLB article looks like it is two two-game series.
Next week's rivalry home-and-home series, in one sense, could be seen as a way to kick off the summer with a format that gives a little taste of the postseason in May for the first time -- two teams going home-and-home consecutively. In another sense, Feeney says it was a key way to get the unprecedented schedule to fit, since there had to be a "squeeze week" -- one week in which every team plays three series -- and the rivals were going to play a pair of two-game series at some point, anyway.
http://mlb.mlb.com/news/article.jsp?ymd=20130523&content_id=48380512&vkey=news_mlb&c_id=mlb