Senior Data Scientist

WHAT WE DO: Zefr is the global leader in brand suitability targeting and measurement across the world's largest platforms. Zefr’s technology is helping to power the age of responsible marketing by putting advertisers in control of their content adjacencies based on their own unique brand safety and suitability preferences, mapped to the Global Alliance of Responsible Media's (GARM) industry standards. As an official YouTube Measurement Program Partner, Meta for Business Partner, and TikTok for Business Partner, the company leverages patented machine learning and AI technology (Cognition AI) to offer brands and agencies more precise and transparent brand safety and suitability activation and measurement solutions on scaled platforms. The company is headquartered in Los Angeles, California, with additional locations across the globe. WHAT YOU’LL DO: We are hiring a Senior Data Scientist focused on the research and productionalization of Large Language Models for multimodal social media content understanding. We work with multi-terabytes of social media platform data from TikTok, YouTube, Facebook, Instagram, and Snap. In this role you will fine-tune, optimize, and deploy LLMs that understand what hundreds of millions of videos, images, and text posts are about. Your work will span the full lifecycle — from research and prototyping to production-grade serving at scale. You will fine-tune LLMs and perform inference optimizations, balancing quality, latency and cost. You will build sophisticated compound AI systems that combine multiple models and modalities into reliable, scalable pipelines. We are excited to welcome someone who is passionate about pushing the boundaries of what LLMs can do and who can keep up with the rapidly evolving landscape of foundation models and inference infrastructure. This is a role where we both expect to learn from you and have you learn from us. Tech stack: - Languages: Python, SQL - Data Stores: Snowflake, Qdrant - Data Processing: Ray, Pandas, DBT, FastAPI, Airflow, Astronomer, DBOS - DevOps: Github Actions, Docker, Terraform, Kubernetes, ArgoCD, AWS, GCP, Datadog - MLOps & Inference: PyTorch, Triton Inference Server, vLLM, Nvidia Dynamo, Nvidia TensorRT LLM, Weights and Biases, Transformers, ONNX, Nvidia TensorRT, DVC, HuggingFace, CUDA, Baseten Inference - Tools: Voxel51, Claude Code, Cursor WHAT WE’RE LOOKING FOR: - Bachelor's or Master's degree in Computer Science or related field with 4+ years of professional experience in machine learning or data science - Hands-on experience fine-tuning large language models (open-source and/or closed-source) - Experience with LLM inference optimization — KV cache management, quantization, multi-node GPU serving, batching strategies, and serving frameworks (vLLM, TensorRT LLM, SGLang) - Track record of taking ML models from research to production at scale - Fluency with Python and SQL (specifically Snowflake) - Experience working with multimodal models and features - Familiarity with cost/quality tradeoff analysis across LLM providers and self-hosted models - Experience with distributed systems and GPU-accelerated workloads - Strong foundation in data structures, algorithms, and software design - Thorough testing and code review standards/practices - Strong verbal and written communication skills - Experience working with Autonomous Coding Agents - Openness to new technologies and creative solutions BENEFITS (FOR US BASED EMPLOYEES): - Flexible PTO - Medical, dental, and vision insurance with FSA options - Company-paid life insurance - Paid parental leave - 401(k) with company match - Professional development opportunities - 13 paid holidays off - In-office, hybrid, and fully-remote work options available - “Summer Fridays” (shorter work days on select Fridays during the summertime) - In-office lunches and lots of free food - Optional in-person and virtual events (we like to celebrate!) COMPENSATION (FOR US BASED EMPLOYEES): The anticipated base salary for t