Principal Research Engineer, Post-Training

• PhD in Computer Science, Machine Learning, AI, or a related field, or equivalent industry 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.

• Deep understanding of modern machine learning techniques, including transformers, reinforcement learning, alignment methods, and large language models.

• Strong track record of delivering impactful research or applied ML systems in production environments.

• Expertise in designing, building, and maintaining production-quality ML systems and infrastructure.

• Experience training, serving, debugging, and optimizing large-scale models on GPU-based systems.

• Experience leading teams working on large language model training, mid-training, or post-training.

• Experience with product experimentation, online evaluation, and A/B testing frameworks.

• Strong software engineering skills with the ability to write clean, maintainable, and scalable code.

• Excellent communication skills and the ability to influence technical direction across teams. Lead complex, cross-functional initiatives across data, training infrastructure, evaluation, and model serving.

• Hands-on experience working directly with open-source models like Mistral and Qwen, particularly adapting them via mid- and post-training for specific personas, creative writing, or role-playing applications.

• Familiarity with cloud-native ML infrastructure, including Kubernetes, Docker, and modern orchestration platforms.

• Publications in leading machine learning conferences or demonstrated contributions to the broader AI community.

Character.AI empowers people to connect, learn and tell stories through interactive entertainment. Over 20 million people visit Character.AI every month, using our technology to supercharge their creativity and imagination. Our platform lets users engage with tens of millions of characters, enjoy unlimited conversations, and embark on infinite adventures.

In just two years, we achieved unicorn status and were honored as Google Play's AI App of the Year—a testament to our innovative technology and visionary approach.

Join us and be a part of establishing this new entertainment paradigm while shaping the future of Consumer AI!

At Character, we value diversity and welcome applicants from all backgrounds. As an equal opportunity employer, we firmly uphold a non-discrimination policy based on race, religion, national origin, gender, sexual orientation, age, veteran status, or disability. Your unique perspectives are vital to our success.