There's a phone screen, a technical phone interview, and then you finally interview at HQ.
The phone screen is pretty straightforward. They ask about projects, interest in company, etc. Then ends it asking you to explain a data structure
The technical phone interview was also pretty easy. Language specific questions such as which language is faster, manual vs auto memory management, and differences between Java/C++/Python. They asked about some projects I worked on as well. Finally, we we coded a really basic problem relating to a trivial property of an array. You can easily do it in O(n). That took less than 10 minutes. We then went on to talk about the company.
Flying out to Philly was interesting. They put you in a wonderful hotel and talk to you over dinner. The interview begins early in the morning. You're put in a room where you'll have 30 minutes to solve a big data problem given the language of your choice. Next, 2 interviewers discuss your solution with you and then move on to more language-specific questions. After, 2 more interviewers ask data structures/algorithms questions, but those were pretty basic, too. You end the day with a tour of the HQ.
Overall, the interview experience was great, but my first interviewer was awful. The worst person I've ever interviewed with. He would consistently ask niche questions from libraries/packages I've never used and grill me me for not knowing them. His tone was condescending and uninterested. In discussing my solution, he actually had a rather negative comment toward it, but no valuable input on how to improve. His interview alone secured my decision to never apply here again.