Principal Data Scientist - ML, Personalization & Growth

Reddit is home to over 100,000 active communities and approximately 130 million daily active unique visitors. Reddit operates a complex consumer ecosystem where users, content, communities, and conversations interact dynamically over time.

We are looking for a senior Principal Data Scientist and thought leader to shape how Reddit understands and optimizes the consumer flywheel. In this role, you will define the measurement, modeling, and experimentation strategies for core consumer questions: how users discover value, form habits, and deepen engagement; how systems personalize and serve user intent; and how algorithms create durable long-term value for contributors, communities, and Reddit.

Partnering across Product, Engineering, Research, and Community organizations, you will transform ambiguous consumer problems into durable analytical frameworks, production-grade machine learning models, and executive product decisions.

Key Responsibilities

• Consumer Scientific Strategy: Set the scientific direction for high-impact consumer domains across discovery, relevance, personalization, retention, user growth, content supply, and community dynamics.
• Ecosystem & User Modeling: Build representation models and frameworks that represent users, content, intent, and community health over multi-step interactions.
• Experimentation & Causal Inference: Steer experimentation strategies to separate durable, long-term improvement from temporary metric spikes. Account for feedback loops, network interference, selection bias, and distribution shifts.
• Heterogeneous Impact Measurement: Build state-of-the-art measurement frameworks to evaluate heterogeneous effects across user personas, acquisition cohorts, content formats, and platform surface areas.
• Product & Executive Influence: Translate complex statistical, deep learning, and causal findings into actionable product strategies, partnering directly with Product, Engineering, and Research leaders.
• Mentorship & Org Leadership: Mentor senior data scientists and research leads, raising technical standards and influencing the broader direction of Reddit's Data Science organization.

Requirements

Domain Expertise & Technical Skills

• Deep expertise in at least one key domain of consumer data science: Recommender Systems, Information Retrieval, Personalization, User LTV/Lifecycle Modeling, Knowledge Graphs, or Causal Inference.
• Advanced proficiency with modern ML methods for behavioral and textual data, including representation learning, sequential models, contextual bandits, or graph neural networks.
• Hands-on experience with deep learning frameworks (PyTorch or JAX).
• Advanced statistical foundations in causal inference, experiment design, variance reduction, and observational studies.

Strategic Leadership & Execution

• Extensive track record of applying data science, machine learning, and experimentation to large-scale consumer digital products.
• Proven technical judgment across model design, multi-objective optimization, validation, and production trade-offs.
• Exceptional written and verbal communication skills with the ability to influence cross-functional executives and clarify complex technical trade-offs.

Benefits & Total Rewards

• Compensation Package: Competitive base salary ($313,000 – $365,100 USD) plus equity grants (RSUs).
• Healthcare & Wellness: Comprehensive medical, dental, and vision health coverage.
• Retirement Savings: 401(k) program with generous employer matching.
• Time Off & Support: Generous paid vacation, parental leave (4+ months paid), and Reddit Global Wellness Days.