Completed the Plaid data engineering loop a couple months ago for a senior DE role. Sharing because data eng interviews vary wildly by company and I spent two weeks prepping for the wrong things.
Here's the actual format: one OA (SQL-heavy), one live coding round, one system design round focused on data pipelines, one behavioral. Four rounds plus the recruiter screen.
The OA SQL: harder than I expected. Not just joins and group-bys. They had a question involving window functions with partitioning, and another that was basically a recursive CTE or a creative use of LAG/LEAD to solve a gap-and-island type problem. If you've been lazy about advanced SQL, sharpen up before applying. I'd say the SQL OA is medium-hard LeetCode equivalent if you calibrate against the SQL section there.
Live coding: Python. A data processing problem. They gave me a dataset-like structure and asked me to transform it, handle edge cases, and then optimize for larger input. Felt like a real data task, not a pure algorithms problem. Understanding pandas would help but they let me use pure Python if I preferred.
System design (the important one): design a financial data pipeline. The context was very Plaid-specific: imagine you're ingesting real-time transaction data from bank connections at scale, normalizing it across inconsistent bank response formats, and serving it reliably to downstream applications. What does that architecture look like?
I talked through: ingestion layer (Kafka for streaming), normalization service (schema registry, handling missing fields), storage (data lake + hot cache for recent transactions), retry logic for failed ingestion, observability. The interviewer pushed hard on "what happens when a bank returns malformed data" and "how do you handle schema drift over time."
Financial data note: they care about auditability. Every pipeline change should be traceable. I mentioned immutable event logs and that landed well.
Total loop: about 5 weeks start to finish. Not lightning fast but not slow. They were communicative.
Comp for senior DE in SF: my offer was around $220-240k TC, mostly salary-heavy with a modest equity component compared to pure SWE roles. Worth asking about equity vesting schedule specifically.