There were 4 rounds - 1) Phone interview with the HR involving behavioral questions and a market sizing question, 2) Phone interview with an associate in similar format, 3) Phone interview with a manager involving experience-related questions and an open-ended distribution cost reduction case and 4) Day-long final round interviews.
The final round was in the Chicago office and started with a brief intro followed by an excel assessment (1 hour), 3 case interviews (which are quite similar to phone interviews but done in-person), a social lunch and a case presentation.
The excel assessment wasn't tough. You just need to know day-to-day excel functions - vlookup, sumif, pivot tables etc. And not get overwhelmed with lot of data but be able to identify what's relevant, stick to the objective and proceed. The 3 case interviews - 45 mins each - were one-on-ones with a manager and 2 senior managers and involved a market sizing question and 2 general supply chain cases. The social lunch was good and you got to meet everyone from managers to partners. The case presentation was challenging. You have 1h15m to prepare. You're given a case handout containing the question, excel data and a company presentation template. The case wasn't tough, but you need to manage time effectively. You have about 15 mins to present your recommendation and analysis. This is followed by 5 mins of Q&A.
The interview process was spread out over 3 months but was completed in a couple of weeks.
The only issue with the process was that a buddy wasn't assigned to me in the few days before the interview. But that wasn't a problem as I knew some people at the firm who shared information about the interview process with me. Overall, the process was smooth.