The process started with a call from the internal recruiter, who understood my profile and assignments. She setup introductory call with a Prinicipal Engineer in Seattle,who was quite responsive and open with his communication. I then had two phone interviews one with a Prinicipal Engineer in Seattle and another a SDE 2 from Bangalore. The first one was easy, focussed on breadth, the second one was on design and architecture. The interviewer was mature and did a good job. It was like a collaborative designing problem. My 1:1 interviews were spread across two days and involved shuttling between two offices of theirs. Couple of these were on basic problem solving and couple were done by senior engineers. I wouldn't consider the interviews tough, but i felt that the interviewers were expecting to be wowed.