If you thought you were going to get to see Ant-Man in Avengers: Infinity War in any real way, you best retire those expectations. Because the MCU's most charming character is likely to be as involved as Hawkeye - in other words, not a lot at all.
Thanks to the prelude comic, we already know that Scott Lang hung up his heroism in the wake of Captain America: Civil War in order to concentrate on looking after his family, and despite the size of Thanos' threat, he's probably going to stay out of the picture for the first half of the big show.
And to reiterate that fact, when asked by the Radio Times about how Ant-Man will tie in to Infinity War, director Joe Russo offered the following:
"Civil War has a big impact on everything that followed it, the events of Civil War. In that movie, there are characters who are on the wrong side of the U.S. government, and so the audiences will get to see how everyone responded to being on the wrong side and what decisions they made that allowed them to move forward in their lives."
Obviously, he's keeping his cards close to his chest in terms of actual Infinity War involvement, but the fact that Russo talks only in terms of Civil War's impact confirms the fact that Ant-Man & The Wasp will seemingly be set (at least at the start) before Infinity War. For that to work fully, he can't appear in Infinity War unless with a huge revelation that is then explained in retrospect in his stand-alone - that would be the traditional story-telling convention for that sort of timeline.
And the point about consequences seems to suggest Ant-Man will be facing government recurpussions, as we've seen in the trailer for the sequel. If he doesn't end up in hiding by the end of his stand-alone, to appear again in Avengers 4, it will be very surprising. Still, it's a shame we won't get to see him in Infinity War.