just finished the Mercury loop and got an offer, so writing this while it's fresh.
Total: 5 rounds over about 3 weeks.
Round 1 recruiter call, 30 min. pretty standard, mostly 'why Mercury, what are you looking for.' She was sharp and direct, no HR pleasantries theater. She told me upfront what the loop would look like and what they actually care about, which I appreciated.
Round 2 hiring manager, 45 min. half background, half product/system thinking. He asked me to walk through a distributed systems decision I made at my last job and then pushed on every tradeoff I named. It felt like a technical Socratic interview. Have specifics ready.
Round 3 coding, 1 hour. not LeetCode-style in the traditional sense. it was a problem grounded in something you'd actually build at a fintech company. I was expected to handle edge cases proactively, not wait to be asked.
Round 4 system design, 1 hour. I did a payments-adjacent design. the interviewer wasn't looking for a textbook answer, they wanted to see how you scoped the problem and where you defaulted to simplicity vs. when you reached for complexity.
Round 5 values/culture, 30 min. this one matters more than you'd think. they asked about low-process environments, working without clear ownership, and making calls with incomplete info. have 2-3 concrete stories ready that aren't just 'I worked really hard.'
turnaround on the offer was 4 days after the final round. team is small, decision-making feels real.