The phone screen was light weight, just background check and so on. The onsite interview was a little bit more serious. The first talk was with 2 heads (one is the boss of the group and one is his boss). Both were pretty friendly without deep technical questions. Then there were 4 2-1 or 3-1 interviews, each 1 hour. Most were technical and some are tough. Covering algorithms / C++ knowledges / behavioral questions. I answered 80% of them.