Did the Unilever senior software engineer final loop last month. The system design round was the one I was most uncertain about going in, because there's almost no info online about what their tech interviews actually look like at senior level.
Here's what the system design interview was like for me.
The prompt: Design a product recommendation engine for an e-commerce platform. Scope was intentionally vague, which I think was the point. They wanted to see if I'd ask clarifying questions before diving in.
Clarifying phase: Spent about 8 minutes asking about scale (DAU, catalog size, latency expectations), personalization requirements vs. rule-based, and whether we're building from scratch or integrating with an existing data warehouse. The interviewer was engaged here. He clearly valued the questions more than a lot of interviewers do.
Design phase: We went through a rough architecture: API gateway, recommendation service, offline model training pipeline, feature store, caching layer. I didn't use a whiteboard (this was on Zoom) so I was describing while sketching in a shared Google doc, which worked fine.
Deep dives: They pushed on two things specifically: how I'd handle cold start for new users, and how I'd ensure the system degrades gracefully if the ML model serving is down (fallback to popularity-based recs). The cold start question got fairly deep into collaborative filtering vs. content-based approaches.
Behavioral overlap: At the end they asked a question about how I'd communicate a major architectural change to non-technical product stakeholders. This blurred into behavioral territory, which is common at senior level.
Total time: about 55 minutes. The interviewer was a principal engineer. Not a relaxed chat but not FAANG brutal either. I'd call it solid mid-market difficulty. If you can do a decent design for a feed system or a search ranking system, you're in the right zone.
For context: role was London-based, Senior Software Engineer in their data and digital platforms org, 2026 hire.