Machine Learning Engineer, Ads Optimization & Ads Marketplace Quality

This role sits in the Ads Optimization and Ads Marketplace Quality (AMQ) organizations, which are responsible for the health and performance of Reddit’s ads marketplace. We focus on:

• Designing the auction and bidding mechanisms that decide which ads show to which users and at what price.
• Building optimization systems that help advertisers achieve their goals (e.g., conversions, ROAS) under budget and delivery constraints.
• Ensuring marketplace quality by improving user experience with ads, fighting ad blindness, and increasing valuable ad opportunities on the platform.

You’ll join a set of tight-knit engineers working on high-impact, internet-scale problems at the core of Reddit’s revenue engine, collaborating closely with Product, Data Science, and Infra partners across Reddit Ads.

We are hiring Machine Learning Engineers (IC3 and 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.
• Own systems end-to-end: from problem formulation and algorithm design to experimentation, production deployment, and ongoing iteration.
• Work across Ads Optimization (bid strategies, budget optimization, pacing) or Ads Marketplace Quality (ad matching, ad load, quality controls) to deliver measurable wins for advertisers and Redditors.

We are hiring at both IC3 and IC4 levels:

• IC3 MLEs are strong individual contributors who can independently own scoped projects, ship models and services, and contribute to experimentation and measurement.
• 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).

• Partner with Ads Marketplace Quality to:
• Improve ad matching and ranking by incorporating new quality and relevance signals into bidding and auction decisions.
• Inform policies around ad load and eligibility that protect user experience while increasing high-quality ad opportunities.
• Collaborate closely with Ads Optimization to integrate new bid strategies and pacing mechanisms into the broader ads ecosystem and measurement stack.

(Level will be determined during the interview process; IC4 expectations assume deeper experience and broader scope.)

• 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.

• 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 (e.g., CTR/CVR, CPA, ROAS)
• 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.

• Evidence of stronger math and optimization skills than a generic MLE, such as:
• Degree or equivalent background in a quantitative field (math, physics, quantitative finance, economics, operations research, or similar).
• Work experience in optimization-heavy domains (e.g., bidding/auctions, pacing, pricing, logistics optimization, quantitative finance).
• Comfort reasoning about and implementing custom optimization logic (e.g., gradient-based methods, constraint handling), not just applying black-box tooling.

• Ads Optimization (bid strategies, conversion/ROAS optimization, pacing and budget allocation)
• Ads Marketplace Quality (ad matching, load, and quality controls)

This job posting may span more than one career level.

In addition to base salary, this job is eligible to receive equity in the form of restricted stock units, and depending on the position offered, it may also be eligible to receive a commission. Additionally, Reddit offers a wide range of benefits to U.S.-based employees, including medical, dental, and vision insurance, 401(k) program with employer match, generous time off for vacation, and parental leave. To learn more, please visit https://www.redditinc.com/careers/.

To provide greater transparency to candidates, we share base salary ranges for all US-based job postings regardless of state. We set standard base pay ranges for all roles based on function, level, and country location, benchmarked against similar stage growth companies. Final offer amounts are determined by multiple factors including, skills, depth of work experience and relevant licenses/credentials, and may vary from the amounts listed below.