Senior Machine Learning Engineer, GenAI Security

## About the Role As a Senior Machine Learning Engineer on the GenAI Security team at Reddit, you will play a pivotal role in developing and implementing machine learning models that protect Reddit's GenAI usage. This includes employee tools, internal agents, and production user-facing systems. The mission of the GenAI Security team is to secure and protect Reddit's AI traffic and GenAI adoption by default, ensuring the integrity and trust of the Reddit community.

The role involves building zero-trust, defense-in-depth systems that verify identity, permissions, data access, and semantic intent across AI workflows. A key part of this work is developing practical, high-quality ML models that detect and prevent security risks such as prompt injection, jailbreak attempts, sensitive data exfiltration, unsafe model behavior, anomalous usage, and unauthorized agent actions.

The Senior Machine Learning Engineer will lead model development for GenAI Security, helping to establish strong ML practices across the Security, Privacy, Assurance, and Corporate Engineering (SPACE) organization. This role owns the full machine learning lifecycle, from problem definition and data ETL to feature engineering, model training, model evaluation, deployment, experimentation, prediction, monitoring, debugging, and retraining.

## What You Will Do - Build and improve security-focused ML models for Reddit’s GenAI traffic, including guardrail models, semantic classifiers, anomaly detection models, and other neural network-based security signals.

• Own model development end-to-end: define the security problem, assemble and label datasets, build ETL pipelines, engineer features, train models, evaluate quality, deploy to production, monitor performance, and retrain from production feedback.
• Utilize modern deep learning architectures, including neural networks, transformers, sequence models, embeddings, and model distillation, where they are the right practical fit.
• Design rigorous evaluation suites for adversarial examples, hard negatives, long-context inputs, structured payloads, tool calls, multi-turn workflows, and real production traffic.
• Improve model precision, recall, latency, cost, calibration, and operational reliability for high-impact production surfaces.
• Build repeatable MLOps workflows for SPACE, including training pipelines, model lineage, artifact management, holdout evaluation, dashboards, rollback paths, and retraining loops.
• Partner closely with ML Infrastructure, LLM Gateway, DevX, Ads, Answers, Safety, Privacy, Compliance, and other Security teams to bring security models into real production workflows.
• Work pragmatically with Reddit’s evolving ML platform, using existing infrastructure where possible and building focused tooling when needed to keep model iteration moving.
• Translate security goals into measurable model outcomes and help partners understand trade-offs between risk reduction, latency, false positives, and product impact.
• Provide technical direction to other engineers and serve as a go-to ML expert for GenAI Security and the broader SPACE organization.

• At least 5 years of experience in machine learning, with a focus on model development, deployment, and maintenance.
• Strong background in deep learning architectures, including neural networks, transformers, and sequence models.
• Experience with model evaluation, including designing and implementing test suites for complex scenarios.
• Proficiency in Python and relevant machine learning frameworks such as TensorFlow or PyTorch.
• Experience with cloud platforms, particularly AWS or GCP, and containerization using Docker.
• Strong understanding of security principles and practices, with the ability to apply these to machine learning models.
• Excellent communication and collaboration skills, with the ability to work effectively with cross-functional teams.

• Familiarity with container orchestration tools like Kubernetes.
• Knowledge of software development best practices, including testing and continuous integration.
• Experience with agile development methodologies and version control systems like Git.

• Opportunity to work on cutting-edge AI security projects with a talented team.
• Comprehensive health, dental, and vision insurance.
• Flexible PTO policy and remote work stipend.
• Access to professional development opportunities, including conferences and training programs.
• A dynamic, supportive work environment that fosters innovation and creativity.
• The chance to make a significant impact on the security of Reddit's community and services.

- Develop a strong portfolio: Showcase your experience in machine learning, especially in the context of AI security. Highlight projects that demonstrate your ability to design, implement, and deploy secure ML models.

• Stay updated on the latest security threats: Continuously educate yourself on emerging threats in AI security and how machine learning can be used to mitigate them. This knowledge will be invaluable during interviews and in your role.
• Focus on collaboration: Given the cross-functional nature of this role, be prepared to discuss your experience working with diverse teams, including security, privacy, and product development teams.
• Prepare to back your claims: Be ready to provide specific examples of your accomplishments, especially in relation to improving model precision, recall, and operational reliability.
• Consider Reddit's unique culture: Familiarize yourself with Reddit's community-driven approach and how this impacts the role of a Senior Machine Learning Engineer in GenAI Security.
• Tailor your application materials: Ensure your resume and cover letter are tailored to the role, emphasizing your machine learning expertise, security knowledge, and experience working in fast-paced, collaborative environments.
• Be ready for technical challenges: Come prepared for technical interviews by reviewing common machine learning concepts, deep learning architectures, and security-related topics.