I applied and I received a HackerRank challenge. The HackerRank question was consisting of only one question. I did not get right the question because the timer was running out, and got right all the test cases except one, had I had 5 mins more I would have fixed that. While I am not into competitive programming (which is what HackerRank tests) I failed because I did not read the question and spent 40 mins doing useless stuff. My advice is to spend some time READING the question. Unfortunately Palantir has decided that it is best for them to evaluate only candidates that pass that coding test. In my opinion is not a good filter, since I found out that I could have simply googled the name of the coding challenge (which name was "Catching an insider trader") and would have found a GitHub repo with the code for the challenge, you just tweak it a bit in a way hacker rank does not catch you and you get a phone interview.

first Online Assessment, which contains 2 medium-easy leetcode style questions and 1 Rest API design. then phone screen, which is a behavioral kind of questions. then Technical leetcode style questions.