Senior Machine Learning Engineer, GenAI Security

We are looking for a Senior Machine Learning Engineer to lead model development for GenAI Security and help establish strong ML practices across SPACE. This role owns the full machine learning lifecycle: problem definition, data ETL, feature engineering, model training, model evaluation, deployment, experimentation, prediction, monitoring, debugging, and retraining.

- 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.

- Use 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 tradeoffs 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 broader SPACE model needs.

- 5+ years of experience building, training, evaluating, and deploying production ML or deep learning models.

- Hands-on experience with modern ML frameworks such as PyTorch, TensorFlow, or similar.

- Strong practical understanding of the full ML lifecycle: problem definition, data ETL, feature engineering, training, evaluation, deployment, monitoring, debugging, and retraining.

- Experience building data pipelines and working with large-scale datasets.

- Experience designing rigorous model evaluations, including precision/recall/F1, false positive analysis, threshold tuning, calibration, holdout sets, regression tests, and production-quality validation.

- Experience shipping production-quality software, preferably in Python and/or Go.

- Strong communication skills and ability to explain model behavior, risk tradeoffs, and technical decisions to cross-functional partners.

- BS degree in Computer Science, Machine Learning, a related technical field, or equivalent practical experience.

- Applying ML to security, privacy, trust and safety, abuse prevention, adversarial ML, or GenAI security problems.

- Training or fine-tuning neural text models for complex inputs such as long-context prompts, structured payloads, code-like content, multi-turn interactions, or tool calls.

- Production MLOps or model serving systems such as Airflow, Ray, MLflow, Triton, ONNX, Kubernetes, or similar.

- Improving model quality through labeling strategy, hard-negative mining, synthetic data generation, distillation, or active learning.