I contacted a recruiter via LinkedIn and was immediately approached by the hiring manager about this role. I went through 2 technical phone screens in the same week and then was called in for an onsite interview a week later. From what the recruiter explained, it seemed that they were looking to hire for the same role in two different teams (which again were working pretty closely). Instead of coordinating between themselves, both the teams decided to have own full-length F2F interview on the same day! I ended up going 13 very technical rounds of 1:1 interviews with different members of the teams!! It started at 9 AM and went on till 6 PM. To say, it was tiring, would definitely be an understatement. The questions were very bookish knowledge-based and I understand that since I wasn't able to remember some of the mathematical formulae, I was not hired. However, I was let down by the overall experience. Not only, was the team the unsympathetic towards grilling a candidate for 9 hours, but the recruiter also did not even have the courtesy to let me know about their decision.