There were 4 rounds of interviews spanning 6 weeks.
The first Interview was just a "fit test" over Skype Call to determine whether you're the right fit for the role with a recruiter who explains what is expected. They request to reveal your expected salary range; I suspect this is to ensure that the appropriate level of an offer is being made later in the stage should they find the role is suitable for you.
The second interview was with the reporting manager for about an hour; asking once again for the "usual" cultural fit tests and a more detailed explanation about the role; also asked for the expectations from your end.
The third interview was the actual Case Study and presentation to the Partner which lasts for about an hour.
The final interview was with another senior partner who spends about 30 minutes with you to ask some of the cultural fit and some technical questions.