Senior Staff Machine Learning Engineer, ML Understanding

Details

Reddit is looking for 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. You will set the technical direction for Reddit's core user representation layer across Feeds, Search, Notifications, and Ads.

Responsibilities

• Define a unified user understanding framework and strategy covering embeddings, tags, attributes, LLM-based user profiles, computation, storage, and exposure.
• Provide technical leadership in user understanding and user modeling by setting a long-term vision and advancing the state of the art.
• Lead the design and implementation of large-scale user representation models, including sequence-based, multi-interest, and multi-task models.
• Build shared representations across Reddit surfaces while balancing latency, cost, and performance.
• Use LLMs and generative AI to develop 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 for adaptive, interpretable, and context-aware personalization.
• Partner with platform teams to 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 support low-latency serving, high availability, and MLOps integration.
• Partner with Feeds, Notifications, Search, and Ads teams to drive experimentation and adoption of new user understanding models.
• Ensure measurable end-to-end impact on product metrics.
• Mentor senior and staff engineers, lead design reviews, steward technical decisions, and champion engineering 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 technical direction and execution.
• Strong product and impact orientation, with an understanding of how machine learning work affects engagement, retention, and revenue metrics.
• Strong fundamentals in representation learning, behavioral modeling, user clustering, and related user understanding approaches, including their real-world trade-offs.
• Experience or strong intuition applying LLMs or foundation models to evolve existing systems beyond incremental improvements.
• Ability to design end-to-end systems spanning data, training, evaluation, serving, and adoption.
• Ability to influence across product, infrastructure, and machine learning teams and align multiple stakeholders.
• Experience mentoring senior engineers, leading design reviews, and establishing best practices for reliable, 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 covering workspace, professional development, and caregiving support.
• Family planning support.
• Gender-affirming care.
• Mental health and coaching benefits.
• Flexible vacation and paid volunteer time off.
• Generous paid parental leave.
• Equity in the form of restricted stock units.

The base salary range for this position is $266,000–$372,400 USD. The role may also be eligible for commission depending on the position offered.