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Principal Research Engineer, Post-Training

About the Role and Team As a Principal Research Engineer on the Post-Training team, you will drive the technical vision, execution, and evolution of the systems that transform foundation models into intelligent, engaging, and aligned produc

Company

Character.AI

Location

Redwood City, CA

Status

Open

Posted

2026-06-22T12:36:20.245+00:00

Character.AI is hiring a Principal Research Engineer to lead its Post-Training team in Redwood City, on-site. The work centers on post-training open-source LLMs such as Mistral and Qwen for role-play chat: alignment algorithms, reinforcement learning, preference optimization and supervised fine-tuning, plus evaluation frameworks, data pipelines and efficient distributed training on GPUs. It asks for a PhD or equivalent experience, a record of leading ML research teams, and production ML systems work. The job pairs technical leadership with mentoring, and names persona and creative-writing adaptation as a nice-to-have.