3 interviews (the last two an hour each) with multiple people asking particular questions about your experience. Lots of hypotheticals and they get into the nitty gritty, so come prepared.
A good candidate should have no problem with this, but beware: before the third interview, they also give you a take-home test that takes an hour+ to complete and will throw out all your qualifications or previous interview answers if they think you didn't do a good enough job on it. They will literally call you out in a snarky way during the job interview over the answers being incorrect, but won't explain what is wrong about them, only inviting you to try it again. Even if you do, you won't get the position, which is a gross thing to do after asking you to spend even more unpaid time on the exam. Their minds get made up quickly, so make sure the test is 1000% correct the first time if you want the role.
Regardless, spending that much time all for naught was an incredibly demoralizing experience. What a waste of energy and effort.