Finished my Moderna loop last month for a mid-level DS role on their clinical analytics team. Sharing because I couldn't find detailed notes anywhere before I went in.
Round count: 5 total. Recruiter call, technical screen with the hiring manager, then a 3-part virtual on-site.
The technical screen was mostly Python and stats. They asked me to walk through a past modeling project, then asked pretty pointed questions about my assumptions. No leetcode, which I appreciated. More like a research conversation.
On-site had three chunks: A data case study. They gave me a messy synthetic clinical dataset and asked me to walk through what I'd explore first and how I'd flag data quality issues. It's open-ended. Narrate your reasoning. Behavioral panel. Two interviewers, back-to-back. Questions were very STAR-structured. "Tell me about a time you had to influence without authority." "Describe a project where the data told you something you didn't want to hear." Real ones. A hiring manager debrief that was half Q&A and half sell. They wanted to know why Moderna specifically and what I knew about the mRNA platform.
The thing that surprised me: they pushed hard on mission fit. Not in a fake way, more like they've had people join who thought it was a stepping stone and didn't stay. So they're filtering for that.
Decision came back in 11 days. Offer was reasonable but not FAANG levels. Worth it for the problem space if that matters to you.