Reddit is a community of communities. It’s built on shared interests, passion, and trust, and is home to the most open and authentic conversations on the internet. Every day, Reddit users submit, vote, and comment on the topics they care most about. With 100,000+ active communities and approximately 126 million daily active unique visitors, Reddit is one of the internet’s largest sources of information. For more information, visit www.redditinc.com. The Feed Relevance team is responsible for the end-to-end systems that power personalization and ranking for the main Reddit feeds. We prioritize building scalable, extensible, and highly performant personalization systems to improve the user experience and drive key business metrics. What You’ll Do As a Senior Staff Machine Learning Systems Engineer, you will help define and lead the vision for the systems that power the Reddit Home Feed. While this role sits within the Feed Relevance team, it is primarily a systems architecture and backend engineering position rather than a modeling role. We are looking for a distributed systems expert to own the 'engines' of personalization—the real-time serving pipelines, low-latency candidate retrieval systems, and high-throughput data fetching layers that allow our models to impact millions of users in milliseconds. * Architect High-Performance Retrieval: Partner with platform teams to design and implement flexible, ultra-low-latency candidate retrieval solutions that balance discovery with computational efficiency. * Optimize the Serving Lifecycle: Design and build "contributor-friendly" serving pipelines that allow backend and product engineers to safely inject logic and features without needing deep ML expertise. * Build Predictive Reliability: Lead the development of sophisticated shadow-testing infrastructure to evaluate distribution shifts and system performance at scale before code ever hits production. * Drive Cross-Stack Integration: Collaborate across the stack—from GraphQL layers to upstream infrastructure—to ensure the feed’s architecture is resilient, maintainable, and extensible. * Performance Engineering: Identify bottlenecks in the feed's ecosystem and implement systemic fixes that improve the user experience. Qualifications: * 10+ years of experience in backend software engineering, with a focus on architecting and scaling high-throughput, low-latency distributed systems for personalization or recommendation engines * Expert-level understanding of distributed systems, including real-time data pipelines, advanced caching strategies (e.g., Redis, Memcached), and storage layer optimization * Proven ability to lead technical strategy across organizational boundaries, partnering with Infrastructure and Platform teams to build extensible, "contributor-friendly" architectures * Adept at navigating complex system trade-offs, such as balancing architectural resilience and latency with the evolving needs of machine learning models * Strong communicator and mentor who leads through collaboration and technical excellence, with experience influencing best practices across a large engineering organization Benefits: * Comprehensive Healthcare Benefits and Income Replacement Programs * 401k with Employer Match * Global Benefit programs that fit your lifestyle, from workspace to professional development to caregiving support * Family Planning Support * Gender-Affirming Care * Mental Health & Coaching Benefits * Flexible Vacation & Paid Volunteer Time Off * Generous Paid Parental Leave  #LI-remote, #LI-JS5 Pay Transparency: 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. The base salary range for this position is: $266,000—$372,400 USD In select roles and locations, the interviews will be recorded, transcribed and summarized by artificial intelligence (AI). You will have the opportunity to opt out of recording, transcription and summarization prior to any scheduled interviews. During the interview, we will collect the following categories of personal information: Identifiers, Professional and Employment-Related Information, Sensory Information (audio/video recording), and any other categories of personal information you choose to share with us. We will use this information to evaluate your application for employment or an independent contractor role, as applicable.  We will not sell your personal information or disclose it to any third party for their marketing purposes.  We will delete any recording of your interview promptly after making a hiring decision.  For more information about how we will handle your personal information, including our retention of it, please refer to our Candidate Privacy Policy for Potential Employees and Contractors. Reddit is proud to be an equal opportunity employer, and is committed to building a workforce representative of the diverse communities we serve.  Reddit is committed to providing reasonable accommodations for qualified individuals with disabilities and disabled veterans in our job application procedures. If, due to a disability, you need an accommodation during the interview process, please let your recruiter know.