I had the same experience. I could not figure out how to use the IDE mode in the new version. Turns out this is a bug. It was not supposed to remove the IDE automatically, instead a user could click on "Keep the antigravity IDE" as shown in the Demo Video (at 1:09 in https://www.youtube.com/watch?v=6C0FjHoN3qE). Clean install and disabling auto update solved the problem.