Applied Researcher

• Partner directly with customers across industries to understand their workflows, identify high-value modeling problems, and define success criteria.
• Develop data preparation and curation pipelines with customer teams, turning domain-specific data and expert feedback into training datasets and representative evaluations.
• Design and run training experiments using techniques such as continued pre-training, supervised fine-tuning, reinforcement learning, and parameter-efficient fine-tuning (PEFT), selecting approaches that fit each customer's goals, data, and compute budget.
• Build evaluation suites, analyze model failures, and iterate on data and training methods to improve quality, reliability, and performance on real customer tasks.
• Work with customer engineers and River's infrastructure team to scale training runs, resolve bottlenecks, and support deployment and ongoing model improvement.
• Turn lessons from customer engagements into reusable training recipes, evaluation tools, and improvements to River's platform.

• BS, MS, or Ph.D. in Computer Science, Machine Learning, Mathematics, or equivalent practical industry experience.
• Strong understanding of modern deep learning architectures and practical experience training, fine-tuning, and evaluating language or multimodal models.
• Extensive hands-on experience with PyTorch or JAX, with a track record of writing clean, scalable code for model training and experimentation.
• Proven ability to turn open-ended problems and imperfect real-world data into working models, using rigorous experiments and evaluation to guide decisions.
• Strong communication and collaboration skills, with the ability to work directly with customers, learn new domains, and explain technical tradeoffs to technical and non-technical audiences.
• A highly collaborative mindset, ownership of outcomes, and a bias for action in a fast-paced environment.

Preferred Qualifications: (We encourage you to apply even if you don't meet all of these)

• Experience delivering models for customer or industry use cases, with measurable improvements in model performance or business outcomes.
• Expertise in reinforcement learning, preference optimization, synthetic data generation, or adapting models to specialized domains.
• Experience with distributed training, experiment management, or deploying and monitoring models in production.
• Experience partnering with domain experts and working with proprietary or sensitive datasets under customer privacy and security requirements.

• Location: Palo Alto, California.
• Compensation: Depending on experience and skills the expected base pay is $200,000 - $420,000 USD per year, plus equity.
• Benefits: Comprehensive health, dental, and vision insurance; unlimited PTO; and relocation assistance as needed.
• Visa Sponsorship: We sponsor visas and are committed to supporting the process for the right candidate.

At River, our mission is to create personal AI owned and shaped by each individual. To achieve this, we are rewriting the entire stack from scratch: personal hardware for local inference, bespoke training infrastructure, next-generation UIs, and frontier deep learning research.

We are scientists, engineers, and builders from the industry's top tech companies and AI labs. We bring a proven track record of scaling consumer systems for hundreds of millions of users and architecting the pre-training infrastructure behind today's frontier models.