Hiring: Principal Research Engineer, Post-Training Company: Character.ai Location: Redwood City, CA Job Posted Time: 2026-09-16 16:59:08 Employment Type: Full-time Target Skills & Keywords: Post-Training, LLMs, Reinforcement Learning, Preference Optimization, Supervised Fine-Tuning, Alignment, Distributed Training, GPU Optimization, Model Evaluation, Data Pipelines, Transformers, Mentorship, Technical Leadership Experience: - Significant experience leading technical projects or teams in machine learning, AI research, or large-scale distributed systems - Experience scaling and mentoring high-performing research and engineering teams - Experience leading teams working on large language model training, mid-training, or post-training - Strong track record of delivering impactful research or applied ML systems in production environments - Experience training, serving, debugging, and optimizing large-scale models on GPU-based systems Required Skills: - Deep understanding of modern machine learning techniques, including transformers, reinforcement learning, alignment methods, and large language models - Expertise in designing, building, and maintaining production-quality ML systems and infrastructure - Proficiency in developing alignment algorithms, optimization techniques, and training objectives - Ability to architect scalable data pipelines and develop robust evaluation frameworks - Strong cross-functional collaboration and technical roadmap leadership Qualifications: - PhD in Computer Science, Machine Learning, AI, or a related field, or equivalent industry experience - Proven ability to define and drive technical roadmaps balancing research innovation with production reliability - Demonstrated success in establishing best practices for experimentation, model development, and deployment Compensation: Not specified in the provided job description. Interested candidates, please apply directly through the job posting on company's career page or try via AI auto apply on this platform. Don’t miss this opportunity to join a forward-thinking team!