Senior Machine Learning Engineer, Model Training and Reinforcement Learning

Role description

Role Overview

Nebius is a leading cloud infrastructure company for the global AI economy. The Senior Machine Learning Engineer will own the infrastructure for large-scale training and RL experiments, making them reliable, reproducible, and efficient. The role sits at the intersection of distributed systems, GPU performance, model training frameworks, RL pipelines, and production engineering.

What You Will Do

Design and run model-training and post-training experiments, build reward functions, judge models, create synthetic data and data pipelines, analyze model-behavior failures, and build and maintain distributed training and RL infrastructure.

Why It Might Be a Fit

The ideal candidate will have strong Python and PyTorch engineering skills, hands-on experience across at least two of model training, post-training/RL, applied modeling, data pipelines, or large-scale ML systems, and the ability to design rigorous experiments with baselines, ablations, metrics, and failure analysis.

Requirements

• Strong Python and PyTorch engineering skills
• Hands-on experience across at least two of: model training, post-training/RL, applied modeling, data pipelines, or large-scale ML systems
• Ability to design rigorous experiments with baselines, ablations, metrics, and failure analysis
• Practical understanding of modern LLM behavior, instruction tuning, preference optimization, and evaluation challenges
• Practical understanding of transformer training bottlenecks, memory pressure, communication overhead, and checkpointing
• Ability to reason quantitatively about model quality, throughput, utilization, reliability, cost, and research velocity
• Strong communication skills and ability to collaborate with researchers, engineers, and leadership

Benefits

• 100% company-paid medical, dental, and vision coverage for employees and families
• Up to 4% company match with immediate vesting for 401(k) plan
• 20 weeks paid parental leave for primary caregivers, 12 weeks for secondary caregivers
• Up to $85/month for remote work reimbursement
• Company-paid short-term, long-term, and life insurance coverage