did the Merck senior SWE system design round in early 2026. took notes immediately after because the format was different from what i expected.
first, some context on leveling. Merck's internal levels don't map cleanly to L5/L6/L7 like Google or the equivalent at Meta. they call the senior IC band something like "principal" depending on the org. for what i interviewed for, they said it was equivalent to "senior" in big-tech terms, which in pharma tends to mean 7-10 YOE.
the system design prompt itself: "design a platform that ingests clinical trial data from multiple sites and makes it queryable by researchers in near-real-time." so domain-adjacent, not generic. i was glad i had some sense of what clinical trial data pipelines look like (site submissions, audit trails, regulatory constraints). if you're interviewing for health tech or regulated-industry roles at Merck, brush up on concepts like data lineage, audit logging, and why you can't just DELETE rows in regulated datasets.
what they cared about most: data ingestion at scale (streaming vs batch, they were fine with either as long as you justified) consistency vs availability tradeoffs for compliance-critical data access control. who can see what. RBAC design came up explicitly. failure modes and how you'd alert on them
what they didn't push hard on: raw latency numbers (this wasn't a low-latency trading system) CDN / front-end delivery cost optimization at massive scale (they're not AWS-scale)
the interviewer was a principal engineer, asked good clarifying questions, wasn't trying to trick me. i ran out of time before covering monitoring in depth and he just said "let's note that and move on" which felt collaborative.
one thing i'd call out: don't assume they want a pure cloud-native microservices answer. they have significant on-prem infrastructure that integrates with cloud. asking "what's the existing environment" in the design round was well-received.
total design round: 60 min. about 10 min scoping, 35 min design, 15 min Q&A. bring questions about the actual platform they're building.