Many announcements came out of Disney's D23 Expo and it seems Pixar has shed some light on the Ant-Man rumor...
Following his presentation this morning at Anaheim's D23 Expo, John Lasseter held a press conference, fielding questions about upcoming projects, including dismissing a rumor that Pixar may be looking at Marvel Studios' Ant-Man and offering a sly "no comment" on potential sequels to other Pixar properties.
"I had met all the folks from Marvel a couple of times and they're terrific. The whole Ant-Man thing is just a rumor."
So...PIXAR is not involved with Ant-Man.