Before giving out any details about interviews, I would like to convey that the company is bad mouthed alot. Don't pay attention to reddit, quora or any other sources. I am sure there are bad expriences but that was in past.
Once you'll talk to their engineers, you'll get to know the cool and impactful stuff they do which matters the most.
The interview process was as follows
Online application -> On their careers page
Hackerrank Test -> They sent out a test, about catching a fraud. It was easy if you can figure out the long story like problem. Once you break down the problem, it was simple algo question.
After the test I was reached for a next round on mail scheduling a phone call. The HR had postponed and this call so many time by not showing up on pre decided time.
HR Screening Round -> Usual Resume break down and questions on Why Palantir ? Why CS major ? Note: Do not take this round and less seriously. Many rejections happen here.
Coding Phone Interview 45min -> Leetcode medium and hard.
Coding Video Interview -> One UI Design + Algorithmic question
Onsite -> 3 Back to back Design, Whiteboard Coding, Decomposition)
Feedback and Rejection Call
[Note: The format for all interviews is introduction, problem solving, ask the interviewer anything]
Random:
My application process was quite long. The online test was around september, and onsite in feb. The HR team is quite tough reach out to during initial phase of the application, though their response time reduces significantly after you've cleared few rounds.