Senior Staff Machine Learning Engineer, ML Understanding

Details

Reddit is seeking a Senior Staff Machine Learning Engineer to lead its next-generation user understanding initiative: building a unified, high-fidelity representation of each user to power personalization across the platform. The role focuses on mainstream machine learning user modeling approaches, including large-scale embeddings, user interest modeling, affinities, and behavioral signals, while applying LLMs and foundation models to improve fidelity, adaptability, and expressiveness.

The engineer will set the technical direction for Reddit's core user representation layer, spanning embeddings, interest modeling, and key user attributes. The systems will support Feeds, Search, Notifications, and Ads, and must be scalable, reliable, low-latency, and widely adopted across product, infrastructure, and downstream machine learning teams.

Responsibilities

• Define a unified user understanding framework and strategy, including how users are represented through embeddings, tags, attributes, and LLM-based user profiles; how representations are computed and stored; and how they are exposed to other systems.
• Provide thought leadership in user understanding and user modeling by setting a long-term technical vision and advancing the state of the art.
• Lead the design and implementation of advanced user models, including large-scale sequence-based, multi-interest, and multi-task representation learning systems.
• Build shared representations across Feeds, Notifications, Search, and Ads while balancing latency, cost, and performance.
• Use LLMs and generative AI to create richer user understanding, including dynamic user profiles, intent inference, and semantic reasoning over user behavior.
• Explore how LLMs can augment or unify embeddings, attributes, and taxonomies to enable more adaptive, interpretable, and context-aware personalization.
• Partner with platform teams to design and build large-scale learning and serving components, including embedding storage and retrieval, feature pipelines, and APIs.
• Collaborate with machine learning and ranking infrastructure teams to ensure low-latency serving, high availability, and integration with MLOps systems.
• Partner with Feeds, Notifications, Search, and Ads teams to drive experimentation and adoption of new user understanding models.
• Drive measurable end-to-end impact on product metrics.
• Mentor senior and staff engineers, lead design reviews, steward technical decisions across the user understanding domain, and champion engineering processes and best practices.

Requirements

• At least 10 years of experience building and scaling production-grade machine learning systems, particularly in user modeling, large-scale representation learning, or recommender systems.
• Experience driving ambiguous, high-impact initiatives from concept through production and shaping both technical direction and execution.
• Strong product and impact orientation, with a focus on improving metrics such as engagement, retention, and revenue.
• Strong fundamentals in representation learning, behavioral modeling, user clustering, and related user understanding machine learning approaches.
• Understanding of trade-offs in real-world machine learning systems.
• Experience with, or strong intuition for, applying LLMs or foundation models to evolve existing systems beyond incremental improvements.
• Systems-oriented thinking across data, training, evaluation, serving, and adoption.
• Ability to influence beyond an immediate team and partner with product, infrastructure, and other machine learning teams.
• Experience mentoring senior engineers, leading design reviews, and establishing best practices for reliable and scalable machine learning systems.
• Comfort navigating trade-offs across quality, latency, cost, and safety in large-scale, user-facing systems.

Benefits

• Comprehensive healthcare benefits and income replacement programs.
• 401(k) with employer match.
• Global benefit programs supporting workspace, professional development, and caregiving.
• Family planning support.
• Gender-affirming care.
• Mental health and coaching benefits.
• Flexible vacation and paid volunteer time off.
• Generous paid parental leave.
• Eligibility for equity in the form of restricted stock units; certain positions may also be eligible to receive a commission.

The base salary range for this position is $266,000–$372,400 USD. Final offers may vary based on skills, depth of experience, and relevant licenses or credentials.