Senior Machine Learning Engineer

Reddit is a community of communities, built on shared interests, passion, and trust, with 100,000+ active communities and approximately 130 million daily active unique visitors. This role sits in the Ads Optimization organization, responsible for the health and performance of Reddit's ads marketplace.

We are hiring Machine Learning Engineers (IC4) to build and evolve the auction, bidding, and budgeting systems that power Reddit Ads. In this role, you will design and implement optimization algorithms for auctions, bidding strategies, and pacing that balance advertiser performance, user experience, and marketplace efficiency. You will own systems end-to-end, from problem formulation and algorithm design to experimentation, production deployment, and ongoing iteration. IC4 MLEs lead more complex or multi-quarter initiatives, set technical direction for key parts of the bidding/auction/pacing stack, and mentor other engineers while remaining hands-on.

• Design and implement models and policies that compute bids for different optimization objectives (e.g., CPC, CPA, ROAS-based strategies).
• Pace budgets smoothly over time across accounts, campaigns, and ad groups while preventing overspend or underspend.
• Allocate spend and auction participation intelligently across segments, surfaces, and time zones.
• Translate product and marketplace goals into concrete optimization problems and constraints (e.g., ROI, revenue, delivery smoothness, fairness, and user experience).

• 3–5+ years of experience building, deploying, and operating machine learning systems in production (for IC4, typically 5+ years).
• Strong programming skills in Python, Java, Go, or similar languages, with solid software engineering fundamentals.
• Experience designing scalable data processing systems (e.g., Spark, Kafka, Airflow, BigQuery, Redis).
• Demonstrated ability to translate ambiguous product or business problems into solutions and to improve measurable metrics.
• Additional expectations for strong bidding/auction candidates: degree or equivalent background in a quantitative field, work experience in optimization-heavy domains, and comfort reasoning about and implementing custom optimization logic.

• Experience with advertising/auction systems, online marketplaces, or search/ranking systems at scale, particularly in bidding, pacing, or budget optimization; auction design, mechanism design, or marketplace quality; campaign performance optimization.
• Familiarity with large-scale, real-time decision systems and low-latency production environments.
• Background in feature engineering, model optimization, and production monitoring for ML systems.
• Experience collaborating with cross-functional partners (Product, DS, Eng) in Ads or marketplace contexts and leading projects from design through rollout.
• Advanced degree (MS or PhD) in Computer Science, Machine Learning, Operations Research, Applied Math, or a related quantitative field.

Base salary range: $216,700—$303,400 USD. Eligible for equity in the form of restricted stock units, and depending on the position, may also be eligible for a commission. Benefits include comprehensive healthcare, 401k with employer match, flexible vacation, paid parental leave, family planning support, gender-affirming care, mental health & coaching benefits, and more.

Apply via the provided Greenhouse link.