I was referred by a friend.
1. Following referral, approximately 2 phone interviews is standard. Questions vary from interviewer to interviewer. In general, they are trying to get to know you/get a feel for if your experience and if you'd fit in the Optimity culture, because maintaining company culture is very important to Optimity and it is one of the great factors that makes them unique.
2. Next step is you'll be called in for a "super day" which is where you will go to Optimity's office and go through several in person interviews with employees from varying levels of experience in their industry and at Optimity. You'll also have a case study interview (sometimes at the beginning or in the middle depending on the availability/schedule of the interviewers). I had the case study first, an interview with an Associate, a Manager, a Senior Manager, and a Partner. Questions again vary from interviewer to interviewer. All except one (the one with a Manager) felt informal. They tried to get to know me, my background, asked typical behavioral interview questions (i.e. - tell me when you had to deal with X situation). Suggest using the STAR method for those kinds of questions (Situation, Task, Action, Result). It doesn't always fit, but it is a good guide to ensure you cover and show your way of thinking and give the interviewers a good understanding of your capabilities, logic, experiences, and communication skills. It is important to relate how your past skills/experiences can be applied to Optimity.
Do your research on the company and talk with employees prior to your interviews if possible, to get a feel for what the company is like, what kinds of projects they work on, and if you feel you'd fit and enjoy your work.