Character.AI

As a Principal Research Engineer on the Post-Training team, you will drive the technical vision, execution, and evolution of systems that transform foundation models into intelligent, engaging, and aligned products. Your team focuses on post-training of top-tier OSS LLMs to power highly immersive role-playing chat features. You will lead initiatives spanning data, algorithms, infrastructure, and evaluation, helping define how our models learn from feedback and improve over time. This is a highly cross-functional role that combines deep technical expertise with organizational leadership, partnering closely with researchers, engineers, product teams, and infrastructure teams to identify the highest-leverage opportunities for improving model performance and user experience. Your work will directly shape the conversational experiences of millions of users daily, influencing both research direction and production systems to build the next generation of AI entertainment.

$275k - $400k

Character.AI is seeking a talented and creative Software Engineer to join its Safety Engineering team. This role is at the forefront of designing, developing, and scaling robust backend systems, leveraging applied machine learning to address critical integrity and safety challenges. You will architect and implement innovative solutions, playing a key role in tackling the unique safety challenges of human-to-AI interaction and defining industry best practices in this emerging space. This is a high-impact position where you will provide technical leadership, drive innovation, and contribute to the core trustworthiness of our platform.

$150k - $300k

As a Software / ML Engineer, you will work cross-functionally with product, data science, and data platform teams to identify, design, and implement applied ML models and infrastructure. This includes model optimization, data pipelines, model training, and serving infrastructure for one of the fastest-growing native AI consumer applications. You will focus on implementing ML backend systems to power discovery surfaces like recommendation, ranking, and search, supporting new AI-generated content formats and optimizing existing systems.

$200k - $300k

Join us as a Research Engineer focused on AI safety and alignment, a critical challenge in today's AI landscape. Your work will be instrumental in understanding and mitigating the risks associated with advanced AI, conducting foundational research to enhance model safety, and solving core technical problems to ensure AI models align with human values and intentions. The Safety team pioneers techniques for more robust, honest, and harmless models. As a Research Engineer, you will translate theoretical research into practical applications, writing high-quality code to test hypotheses and integrate safety solutions into our products, contributing to user protection and the broader AI safety community.

$225k - $400k

Character.AI is seeking experienced Machine Learning Infrastructure Engineers to design, build, and maintain the training and serving infrastructure for ML research. This role involves providing essential infrastructure support to our ML research and product teams, developing tools to diagnose cluster issues and hardware failures, monitoring deployments, managing experiments, and optimizing GPU allocation and utilization for both serving and training. Join us to be part of establishing a new entertainment paradigm and shaping the future of Consumer AI.

$150k - $350k

Joining Character.AI as a Research Engineer on the Post-Training team, you will focus on fine-tuning AI models, optimizing their performance, and ensuring high quality and efficiency. Your work will directly contribute to groundbreaking advancements in AI, shaping an era where technology acts as a companion. The Post-Training team develops powerful pretrained language models into intelligent, engaging, and aligned products. You will work across teams and the technical stack to improve model performance and training methods, impacting the conversational experience of millions of users daily.

$225k - $400k