TL;DR – Really thorough interview process. They know what they want, and you will enjoy talking to them. Interviewing at C3 has been one of the best interview experiences (and the longest) I have had. I am writing this review when I still have three more rounds to go. So, I don’t know the decision at the time of writing this and my review is as unbiased as it can be (I hope so at least). Their interviews are well designed, and the questions make a lot of sense. I have given data science tests with questions on economics (really bad planning on the part of the company). These guys are serious about who they hire and look for a cultural fit more than your technical knowledge. Why you want to work at C3 is the most important question. The interviewers are very helpful and will coach you about the next rounds and so is the HR. They love talking about their own experiences at C3, if you ask them. They get 2000 applications for one position, so the process may be a little slow. The entire process took about 3 months – 1. Employee Referral – Early Jan 2. Hacker Rank Test – Mid Jan – 1 hour – two weeks time a. Part One – Around 10 ML based MCQ’s. Pretty basic stuff. Decision trees, SVM, Logistic Regression, some basic neural networks. b. Part Two – Simple coding test (I chose Python). Took me about 5 minutes to do it (and I am not from a CS background) – the HackerRank IDE is not the easiest to use, so practice a few questions prior to the test. c. If you don’t receive a rejection within 24 hrs of submitting the test, you have cleared it. 3. Phone Screen with two Data Scientists – Mid Feb – 30 min a. Basic resume questions. b. Why C3 – this is a really important question for them, so prepare properly. c. Why did you use random forest for this project? 4. Next 3 rounds were in the same day via Skype. All are knockout, so you may not move onto the next round despite having a time slot – Mid May – 30 to 45 min each a. Round 1 – Shared coding exercise in Python. i. Prepare properly for this as well. ii. Coding on notepad; no code completion available. iii. They will help you through the problem; so, think out aloud. iv. Just coding it is not enough, explaining your thinking is more important. v. I was able to code around 80% of what they wanted, and verbally explained whatever I could not code. vi. Why C3? b. Round 2 – Machine Learning / Resume i. Explain ML projects. ii. Case Study – How would you explain linear regression to a client. iii. Some common practical errors during ML and how to resolve them. c. Round 3 – Machine Learning Technical i. Asked me lots of theory questions ii. Performance v/s accuracy, bagging v/s boosting etc. iii. Case Study – Predictive maintenance on cars. iv. Was told that I will hear back in one to two weeks. (If cleared) The next three rounds will be with the CTO, CEO etc. (mostly behavioral).