Which build tool ionic v3/4 use?

I’m currently upgrade from v1 to v4.
I cannot figure/google out which build tool ionic framework v3/4 use to build bundles? webpack, gulp …?

Ionic uses the Angular CLI to build its projects.
Angular uses webpack to build, so Ionic uses webpack under the hood
–> https://angular.io/cli/build

MattE, Thanks for your information!:+1:
The webpack configuration file is buried in @angular-devkit\build-webpack\src\webpack