I was contacted via LinkedIn last year and did not make it past the phone screen. I was contacted again via Linkedin this year and made it to the on-site interview stage. Overall, the recruiting process seemed efficient and timely - the longest I had to wait for follow-up was the week it took for them to get back to me with the rejection.
Recruiter call: Lasted about 30 minutes and was very pleasant and conversational in nature. Mostly discussed my background and interests.
Phone screen via Skype: Lasted about 45 minutes. As others described, it focused heavily on weaknesses and dug deep into the "why" behind your decisions. It seems like they follow a very strict methodology in terms of who they are looking to hire (felt like they were checking off boxes while interviewing me). It wasn't sufficient to provide a "X was the problem, Y was the approach I took, and Z was the outcome" response to questions. Instead, the questions were very psychological in nature as a means to evaluate decision-making skills and innate thought process. I got off the phone feeling like the conversation went okay, but I was not expecting a call back.
On-site interview: Surprisingly, the day after the Skype call, they invited me for an on-site interview (somewhere around this time I also completed an analytical challenge that tested Excel skills. They gave me 24 hours to submit - not super hard). They covered two nights of stay, which was a nice perk. I interviewed with two individuals (1:1) and had an informal lunch interview as well.
The first interview was behavioral and was very similar to the previous Skype interview, except they dug much deeper into my answers. Unsurprisingly, it seemed like they were less interested in my skills and more interested in my failures and weaknesses as a way to gauge my openness. This was evidenced by the fact that they shot down my initial "what is your weakness" response and told me to try again. Overall, it seemed like the interviewer really liked my responses given the positive reactions.
The second interview was analytical and involved three questions. The case question did not involve any whiteboarding or math, but sought to assess how you would think through a problem and collect data. It was relevant to my background and was not as difficult as I expected. The final question was related to Palantir's product and how you would evaluate its health.
The third interview was an informal lunch, where they take you to their cafeteria and let you chat with an employee.
All interviewers emphasized that this was not a lifestyle job and the hours can be excessive. They also maintain a relatively flat organization, which has its ups and downs. For instance, there is no formal promotion process or a "boss" per se. Everyone pulls their weight, takes full ownership of their work and decries corporate/bureaucratic culture and working for behemoth organizations.
After the lunch, I was let go. One week later, I received a phone call with a generic rejection and no further details on why the decision was made, due to "legal" reasons. After doing some research, it does seem that if they do not keep you past lunch, then they've already decided not to give you an offer (hence, my whole theory on their secretive methodology used to determine the right fit). My understanding is that they no longer require the founder interview (though they may still do it), but at the very least you should get a product demo on-site. When or how they make that decision while you are still in the on-site interview is beyond me. Ultimately, it's difficult to say what the "magic sauce" is they are looking for, but I definitely ended the process feeling quite confused as my answers to the Skype call questions (which I passed) were not wholly different in nature than my answers during the on-site. In fact, I felt that my on-site performance was stronger. *kanye shrug*