Principal Research Engineer, Post-Training

About the role

As a Principal Research Engineer on the Post-Training team, you will shape the technical vision and execution of systems that turn foundation models into engaging, aligned products. Your work will directly influence the conversational experience of millions of users on Character.AI.

Key responsibilities

• Define and drive the technical roadmap for mid‑ and post‑training systems, balancing research innovation with production reliability.
• Lead development of alignment algorithms, optimization techniques, and training objectives for large language models.
• Architect scalable data pipelines and efficient training/inference infrastructure for large‑scale generative models.
• Partner with researchers, product, and infrastructure teams to identify high‑leverage opportunities and improve model performance.

Required profile

• PhD in Computer Science, Machine Learning, AI, or equivalent industry experience.
• Significant experience leading technical projects or teams in ML, AI research, or large‑scale distributed systems.
• Proven track record of delivering impactful research or production ML systems.
• Strong communication skills and ability to influence technical direction across teams.

Required skills

• Transformers and large language models.
• Reinforcement learning and alignment methods.
• GPU‑based systems and distributed training.
• Kubernetes, Docker, and cloud‑native ML infrastructure.
• A/B testing frameworks and online evaluation.