Just wrapped a senior/staff-level loop at State Street and want to document the system design piece specifically because there's almost nothing out there on it.
First: the scope. They're not asking you to design Uber or Twitter. The prompts are finance-adjacent. My prompt was something like: design a system that processes end-of-day fund NAV calculations and makes them available to downstream reporting systems within a defined SLA window.
That sounds domain-specific but it's mostly a data pipeline design problem. The concepts that came up: Idempotency and exactly-once processing (this was a major theme) Queue-based work distribution vs. batch processing tradeoffs How you'd handle retries and dead-letter queues without double-counting Observability: how do you know a calculation is stale or wrong before the SLA expires Data contracts between services
They're not testing whether you know finance. They explain the domain enough for you to solve it as an engineering problem. What they're testing is whether you can reason about reliability in a regulated environment where wrong numbers are genuinely a big deal.
What tripped me up: I went too fast to the happy path. The interviewer kept asking "what happens if X fails here" and I kept giving the correct answer but not proactively surfacing failure modes myself. After the loop I realized that at State Street, proactively identifying failure modes and audit trails is a signal they weight heavily. It's not just good distributed systems thinking, it's how their engineers actually have to operate.
What landed well: When I proposed writing all state transitions to an append-only log before taking any action, the interviewer noticeably engaged more. That pattern fits their compliance mentality.
Level calibration: I was interviewing for senior (principal-equivalent in their internal leveling). Staff-track candidates might face a harder scope and more emphasis on cross-team design decisions.
Took about a week to get feedback after the onsite. They said the design was strong but they were going to offer me at the senior band not staff because I didn't demonstrate enough organizational influence examples in the behavioral rounds. So the levels conversation here extends into the behavioral component, not just technical.