Senior Research Engineer, LLM Training & Post-Training

Senior Research Engineer, LLM Training & Post-Training

New York, New York, United States; Remote; San Francisco, California, United States; Seattle, Washington, United States

Who We Are

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 Firstminute.

The Way We Work

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.

What We're Looking For

We're are looking for an experienced Senior Research Engineer who has built, trained, and optimized modern transformer-based language models to join our Research Engineering function at Lightning.

This role will focus on advancing how large language models are trained, fine‑tuned, evaluated, and deployed across Lightning AI’s platform and real‑world customer workloads. It will work across model training, post‑training, PyTorch, distributed systems, and AI systems engineering to improve model quality, training efficiency, and developer productivity while collaborating closely with researchers, infrastructure engineers, and customers.

We're looking for someone who enjoys turning cutting‑edge research into production systems. You have deep experience training and improving transformer‑based language models, strong software engineering fundamentals, and a passion for solving difficult problems across model training, evaluation, and AI systems. Rather than building applications on top of existing models, you’re motivated by improving the models themselves and the systems that power them. Our work spans models that power the Lightning AI platform, customer‑specific model workloads, and research that translates into reusable training and platform capabilities.

This role is hybrid with a minimum of 2 in‑office days per week in San Francisco, Seattle, NYC, or London, with fully remote work considered for candidates outside of our office hub locations. All employees participate in occasional team and company off‑sites.

What You’ll Do

• 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

What You’ll Need

Required Qualifications

• 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

Ideal Experience

Experience with one or more of the following:

• DeepSpeed, FSDP, Megatron‑LM, Hugging Face Transformers, TRL, PEFT, Lightning Fabric, or similar training frameworks.
• CUDA, Triton, vLLM, SGLang, TensorRT, or other AI systems and performance optimization technologies.
• GPU performance optimization, mixed precision, memory optimization, or distributed training optimization.
• Open‑source contributions, research publications, or production AI platforms supporting large‑scale training or inference workloads.
• Startup experience or experience working on highly cross‑functional engineering teams.

Compensation

We are committed to offering competitive compensation that reflects the value each team member brings to our mission. Final offers are based on factors such as experience, skills, geographic location, and role expectations. In addition to base salary, our total rewards package for eligible roles includes a discretionary bonus, a meaningful equity component, and comprehensive benefits.

The anticipated annual base salary range for this role is:

$165,000 - $310,000 USD

Benefits and Perks

We offer a comprehensive and competitive benefits package designed to support our employees’s health, well‑being, and long‑term success:

• Comprehensive Health Coverage : Medical, dental, and vision coverage for employees and eligible dependents.
• Meaningful Equity : RSUs that give employees a stake in the company’s long‑term success.
• Retirement Savings : 401(k) matching (U.S.) and pension contributions (U.K.).
• Flexible Time Off : Unlimited PTO, company holidays, and floating holidays to support work‑life balance.
• Company‑Wide Winter Break : Two weeks of company closure each winter to disconnect and recharge.
• Paid Parental & Family Leave : Paid leave to support you and your family through life's important moments.
• Professional Development : Annual learning and development allowance to support your professional growth.
• Wellness Benefits : Wellness and work‑from‑home stipends to support your physical and mental well‑being.
• Sabbatical Program : Four weeks of paid sabbatical leave after four years of service.
• Flexible Work : Flexible schedules and a hybrid work model for our office‑based teams.
• In‑Office Meals : Complimentary meals at our office hubs.

Benefits may vary by location, team, and role.

At Lightning AI, we are committed to fostering an inclusive and diverse workplace. We believe that diverse teams drive innovation and create better products. We provide equal employment opportunities to all employees and applicants without regard to race, color, religion, gender, sexual orientation, gender identity, national origin, age, disability, veteran status, or any other protected characteristic. We are dedicated to building a culture where everyone can thrive and contribute to their fullest potential.

Voluntary Self‑Identification

For government reporting purposes, we ask candidates to respond to the below self‑identification survey.Completion of the form is entirely voluntary. Whatever your decision, it will not be considered in the hiringprocess or thereafter. Any information that you do provide will be recorded and maintained in aconfidential file.

As set forth in Lightning AI’s Equal Employment Opportunity policy,we do not discriminate on the basis of any protected group status under any applicable law.

If you believe you belong to any of the categories of protected veterans listed below, please indicate by making the appropriate selection.As a government contractor subject to the Vietnam Era Veterans Readjustment Assistance Act (VEVRAA), we request this information in order to measurethe effectiveness of the outreach and positive recruitment efforts we undertake pursuant to VEVRAA. Classification of protected categoriesis as follows:

A "disabled veteran" is one of the following: a veteran of the U.S. military, ground, naval or air service who is entitled to compensation (or who but for the receipt of military retired pay would be entitled to compensation) under laws administered by the Secretary of Veterans Affairs; or a person who was discharged or released from active duty because of a service‑connected disability.

A "recently separated veteran" means any veteran during the three‑year period beginning on the date of such veteran's discharge or release from active duty in the U.S. military, ground, naval, or air service.

An "active duty wartime or campaign badge veteran" means a veteran who served on active duty in the U.S. military, ground, naval or air service during a war, or in a campaign or expedition for which a campaign badge has been authorized under the laws administered by the Department of Defense.

A "Armed forces service medal veteran" means a veteran who, while serving on active duty in the U.S. military, ground, naval or air service, participated in a United States military operation for which an Armed Forces service medal was awarded pursuant to Executive Order 12985.

Select...

Voluntary Self‑Identification of Disability

Form CC-305

Page 1 of 1

OMB Control Number 1250-0005

Expires 07/31/2029

We are a federal contractor or subcontractor. The law requires us to provide equal employment opportunity to qualified people with disabilities. We have a goal of having at least 7% of our workers as people with disabilities. The law says we must measure our progress towards this goal. To do this, we must ask applicants and employees if they have a disability or have ever had one. People can become disabled, so we need to ask this question at least every five years.

How do you know if you have a disability?

A disability is a condition that substantially limits one or more of your “major life activities.” If you have or have ever had such a condition, you are a person with a disability. Disabilities include, but are not limited to:

• Alcohol or other substance use disorder (not currently using drugs illegally)
• Autoimmune disorder, for example, lupus, fibromyalgia, rheumatoid arthritis, HIV/AIDS
• Blind or low vision
• Cancer (past or present)
• Cardiovascular or heart disease
• Celiac disease
• Cerebral palsy
• Deaf or serious difficulty hearing
• Diabetes
• Disfigurement, for example, disfigurement caused by burns, wounds, accidents, or congenital disorders
• Epilepsy or other seizure disorder
• Gastrointestinal disorders, for example, Crohn's Disease, irritable bowel syndrome
• Intellectual or developmental disability
• Mental health conditions, for example, depression, bipolar disorder, anxiety disorder, schizophrenia, PTSD
• Missing limbs or partially missing limbs
• Mobility impairment, benefiting from the use of a wheelchair, scooter, walker, leg brace(s) and/or other supports
• Nervous system condition, for example, migraine headaches, Parkinson’s disease, multiple sclerosis (MS)
• Neurodivergence, for example, attention‑deficit/hyperactivity disorder (ADHD), autism spectrum disorder, dyslexia, dyspraxia, other learning disabilities
• Partial or complete paralysis (any cause)
• Pulmonary or respiratory conditions, for example, tuberculosis, asthma, emphysema
• Short stature (dwarfism)
• Traumatic brain injury

Disability Status Select...

PUBLIC BURDEN STATEMENT: According to the Paperwork Reduction Act of 1995 no persons are required to respond to a collection of information unless such collection displays a valid OMB control number. This survey should take about 5 minutes to complete.