went through the full Merck SWE loop earlier this year for a senior backend role out of their Rahway, NJ tech hub. posting the breakdown because the info online is sparse.
stage 1: recruiter screen, 30 min. standard background stuff, they asked why pharma, nothing tricky. recruiter was efficient.
stage 2: online assessment via HackerRank. two coding problems, 90 minutes. i'd describe the difficulty as LeetCode medium, leaning toward graph/tree traversal. one string manipulation question, one that was basically a BFS variant on a grid. no system design here at all.
stage 3: technical phone screen, 45 min with a senior engineer. they did one coding problem (again medium difficulty) plus some quick design questions. nothing deep on architecture, more like "how would you approach caching this" than a full system design session.
stage 4: virtual onsite, 4 rounds over one day. round 1: coding (two problems, similar level to OA) round 2: system design, 60 min round 3: behavioral, about 45 min round 4: hiring manager conversation
total time from application to offer: about 7 weeks. debrief feedback came back within a week of onsite, which is fast for a large pharma company. they were organized about scheduling.
a few things that stood out. the interviewers were genuinely interested in discussing tradeoffs, not gotcha answers. when i asked about the tech stack, the honest answer was Java microservices, some Python for data pipelines, and they're slowly modernizing legacy systems. if you're coming from a pure cloud-native background be prepared to hear about legacy constraints.
tip for the loop: they care about communication and structured thinking as much as raw coding speed. narrate your approach before you write code. i saw one panel note "talks through problems well" as explicit positive feedback.