The interview process at Citadel was intense and comprehensive. The initial phone screen lasted 45 minutes, focusing heavily on probability puzzles and market scenarios. The interviewer was direct and expected quick, accurate responses. Two days later, I had back-to-back video interviews. The first centered on algorithmic trading concepts and Python implementation. The second delved into statistics and machine learning, including detailed discussions about time series analysis. The on-site portion was grueling - six hours of continuous interviews. Notable was an interview with a senior quant who rapid-fired mental math questions for 30 straight minutes. Another session involved debugging complex C++ code while explaining my thought process. The most challenging aspect was a two-hour simulation where I had to develop and defend a trading strategy using real market data. The interviewers deliberately pressured me to test stress handling. The final round with the team lead focused surprisingly more on collaboration style and research approach than technical skills. They emphasized their flat hierarchy and intense work culture.