Position was local in their Georgetown office. The process overall was not much different than other companies, but there were some troubling oddities. Despite their reputation for hard interviews, this was an average experience. Recruiter reached out to me, did a phone screen with someone from California, then someone from the UK called to do interview prep for an on-site, then came the on-site. I met with four different engineers separately who all asked similar questions. I had to whiteboard a solution to a problem, was pounded with Linux cli questions like a contestant on Jeopardy, and had to describe various "what would you do" scenarios.
As for the oddities...For starters, they kept pushing an attitude of "We're the greatest company ever. Be honored we reached out to you." You can see this in their literature, their phone screens, and even the front desk greeter. I never even heard of Palantir before the recruiter reached out to me, and the first three news search results online were related to diversity problems, gender discrimination, and public trust issues surrounding misuse of personal data. I was very uncomfortable when they insisted they take a photo of me for my "candidate profile". When I left, they told me to keep the ID badge and gave me a Palantir-branded packet with Palantir paper and pens inside. In the end, they declined an offer saying I wasn't experienced enough even though I possess a number of relevant high-level certifications, a security clearance, and a lengthy track record of success working for the best companies in technology. I was not disappointed because they left an uninspiring impression, and I would not have accepted the position if offered.