Senior Research Engineer, LLM Training & Post-Training

Senior Research Engineer, LLM Training & Post-Training

Lightning AI is the company behind PyTorch Lightning. Founded in 2019, we build an end-to-end platform for developing, training, and deploying AI systems—designed to take ideas from research to production with less friction.

Through our merger with Voltage Park, a neocloud and AI Factory, Lightning AI combines developer-first software with cost-efficient, large-scale compute. Teams get the tools they need for experimentation, training, and production inference, with security, observability, and control built in.

We serve solo researchers, startups, and large enterprises. Lightning AI operates globally with offices in New York City, San Francisco, Seattle, and London, and is backed by Coatue, Index Ventures, Bain Capital Ventures, and First minute.

The people who thrive here are builders who move fast, communicate openly, take ownership, and continuously improve themselves, their teams, and our company. Here's what that looks like in practice:

• Move with Urgency:
  We move quickly, make thoughtful decisions, and keep momentum. We value action over perfection and learn by shipping.
• Take Ownership:
  We own outcomes, not just our individual work. We make decisions that move the company forward and follow through.
• Communicate Openly:
  We communicate directly, seek to understand, and create clarity for others. Honest conversations help us move faster together.
• Build Great Teams:
  We lead by example, empower others, and create healthy teams where people can do their best work.
• Raise the Bar:
  We're always improving ourselves. We learn from feedback, consistently challenge ourselves to grow, and focus on the work that matters most.
• Think Long-Term:
  We design for what's next. We create scalable systems, simplify complexity, and use AI and automation to amplify our impact.

• Design, build, and optimize training and post-training pipelines for large language models.
• Improve model quality through supervised fine-tuning, continued pretraining, preference optimization, reinforcement learning, evaluation, and experimentation.
• Build and improve PyTorch-based training infrastructure, tooling, and developer workflows.
• Optimize distributed training across multi-GPU environments by improving throughput, memory efficiency, scalability, and GPU utilization.
• Investigate challenging model training issues, including convergence, instability, communication overhead, and performance bottlenecks.
• Design evaluation methodologies, benchmark models, analyze failure modes, and guide model improvements through experimentation.
• Collaborate directly with customers to understand real-world workloads and translate those learnings into improvements across Lightning AI's research platform.
• Partner closely with research, infrastructure, and platform engineering teams to build production-ready AI systems.
• Contribute to open-source projects through new features, tooling improvements, documentation, and community engagement

• Significant experience training, fine-tuning, evaluating, and optimizing transformer-based language models using PyTorch.
• Experience with modern LLM training and post-training techniques such as continued pretraining, SFT, RLHF, preference optimization (DPO, PPO, GRPO), reward modeling, or similar approaches.
• Strong understanding of distributed training and multi-GPU systems, with experience improving training performance, scalability, or efficiency.
• Strong software engineering fundamentals, including building production-quality Python software and research tooling.
• Experience designing experiments, evaluating model performance, and debugging complex training or optimization issues.
• Excellent communication and collaboration skills, including the ability to work effectively across research, product, infrastructure, and customer-facing engagements.
• Comfortable working in fast-moving, ambiguous environments where priorities evolve over time.
• Master's degree, PhD, or equivalent industry experience in Machine Learning, AI, Computer Science, or a related field

Experience with one or more of the following:

• Deep Speed, FSDP,…