Senior

Own the auction, bidding, and pacing algorithms that power Reddit's ads marketplace

Reddit is hiring an IC3/IC4 Machine Learning Engineer to design and ship the optimization algorithms behind its ad auctions, bidding strategies, and budget pacing. Expect deep discussion of ML systems in production, optimization math, and how you'd translate business goals like ROAS into constrained optimization problems.

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What this interview tests

Auction & bidding mechanism design
Budget pacing and spend allocation under constraints
Translating business objectives (ROAS, CPA, CTR/CVR) into optimization problems
Production ML system ownership (design through deployment and iteration)
Scalable data infrastructure (Spark, Kafka, Airflow, BigQuery, Redis)
Marketplace quality (ad matching, ad load, relevance signals)

Common question themes

Design a bidding algorithm for a ROAS-based advertiser objective

How would you pace an advertiser's budget smoothly across a day without overspend

Formulate ad load/quality trade-offs as a constrained optimization problem

Walk through an ML system you took from problem formulation to production

How do you validate an auction change didn't hurt user experience

Gradient-based or custom optimization logic you've implemented beyond off-the-shelf tooling

How candidates describe it

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