Principal Research Engineer, Post-Training

Responsibilities

• Drive the technical vision and roadmap for mid- and post-training systems to transform foundation models into engaging products.
• Lead the development of alignment algorithms, reinforcement learning, and optimization techniques to improve model behavior and safety.
• Mentor and grow a team of researchers and engineers through technical guidance and design reviews.
• Architect scalable data pipelines and efficient training/inference systems for large-scale generative models.
• Partner with infrastructure and product teams to optimize GPU utilization and model observability.

Requirements

• PhD in Computer Science, Machine Learning, AI, or equivalent industry experience.
• Significant experience leading ML research or large-scale distributed systems teams.
• Deep understanding of transformers, reinforcement learning, and alignment methods.
• Proven track record of delivering impactful production ML systems.
• Expertise in GPU-based model training, optimization, and debugging.
• Strong software engineering skills with the ability to write clean, scalable code.
• Experience with product experimentation, online evaluation, and A/B testing.

Preferred Qualifications

• Hands-on experience adapting open-source models like Mistral and Qwen for specific personas or role-playing.
• Familiarity with cloud-native ML infrastructure, including Kubernetes and Docker.
• Publications in leading machine learning conferences.

Benefits

• Competitive compensation: $275K – $400K.
• Top-notch health coverage for you and your family.
• Generous 401(K) contributions.
• Up to 20 weeks of paid parental leave.
• 4 weeks of PTO.
• Daily in-office catering and a monthly DoorDash stipend.
• Monthly wellness stipend.

About the Company

Character.AI empowers people to connect, learn, and tell stories through interactive entertainment. With over 20 million monthly visitors, our platform allows users to engage with tens of millions of characters for infinite adventures. We are a fast-growing unicorn dedicated to shaping the future of Consumer AI.