went through the Reddit DS loop for a senior data scientist role a few months back. the process is well-defined and i thought the quality of the questions was actually high. here's what i encountered.
the loop (virtual, 5 rounds total):
SQL round (60 min). two problems. the first was medium complexity: filter, aggregate, window function. the second was harder: required a self-join and some conditional logic to answer a behavioral question about user retention. you write in a live SQL editor they provide. they can see your screen.
things that matter: don't just write the query. talk through your logic first, say what you're checking for. and read the output carefully before saying you're done. i had a row duplication issue in the second query i caught by inspecting the result set, which they noted positively.
stats and probability round (45 min). two interviewers. topics i hit: A/B test design (they gave me a scenario about testing a new ranking signal and asked me to design the experiment from scratch), Bayesian vs. frequentist framing briefly, one question about Simpson's paradox in the context of a community metric. nothing requiring deep math, but you need to be sharp on the concepts and comfortable explaining them without a whiteboard.
product case round (45 min). 'Reddit is seeing a decline in average comment length on a major subreddit. walk me through how you'd diagnose this.' classic DS diagnostic. start with data quality checks, move to hypothesis generation, prioritize hypotheses by likelihood and testability. they want to see structured thinking, not instant insight.
ML/modeling round (45 min, senior-specific). they asked about ranking models, feature engineering for recommendation, and how i'd handle cold-start. this is relevant because Reddit's core product is basically a ranking problem.
behavioral. standard STAR format. include impact numbers.
overall: the SQL and product case rounds are the filters. if those are strong, the rest is closer to a conversation. comp for senior DS in SF was competitive with market rates as of early 2026.