"Marvel and Edgar Wright jointly announced today that the studio and director have parted ways on Ant-Man due to differences in their vision of the film. The decision to move on is amicable and does not impact the release date on July 17, 2015. A new director will be announced shortly."
Variety reports that the studio has already found a replacement, so it seems this departure may have been in the works for some time now.
The director also co-wrote the screenplay with Joe Cornish, so it's possible Marvel Studios will seek out a new writer as well.
Ant-Man comes to theaters July 17th, 2015 and stars Paul Rudd, Michael Douglas, Michael Pena, Clifton Collins Jr., Evangeline Lilly, Patrick Wilson, Corey Stoll.