How does these instagram Saas works ?

Hey guys, how does these instagram Saas works ? I mean, they offer: followers, etc but i don't know how they work.
most of then asks for instagram username and password so i guess they are not using instagram api. My guess is that they are running multiple selenium headless browsers on their server. is that correct ?
is there another way to offer such services nowadays ?

I would say that is most likely, definately not using API's, sockets would be too easy to detect, selenium is what i have been using the last year or so for the human emulation factor.

I'm assuming your asking about SaaS Instagram automation? If so then yes, they're either running headless browsers or emulating the app.