It was an entire day meeting with managers from a variety of teams. The interview was quite grueling, but fair. They are extremely focused on ensuring that they hire top talent, so they understandably want to be thorough about it. Be prepared to do a LOT of whiteboard coding. You need to be able to explain performance characteristics, code testability, feasibility of algorithms in a production environment, etc. There will be quite a lot of conversation about CS fundamentals, data structures, and algorithms. Strongly recommend pulling out some college textbooks or going through some interview preparation material if you don't feel confident about these things. Some of the problems are designed to be almost impossible to solve in the time provided - they are more interested in seeing your thought process, so don't get too frustrated during the process.