Principal Engineer - AI/ML

About Quizlet:
At Quizlet, our mission is to help every learner achieve their outcomes in the most effective and delightful way. We’re a $1B+ learning platform used by two-thirds of U.S. high school students and half of college students, powering over 1 billion learning interactions each week.
We blend cognitive science with machine learning to personalize and enhance the learning experience for students, professionals, and lifelong learners alike. We’re energized by the potential to power more learners through multiple approaches and various tools.
Let’s Build the Future of LearningJoin us to design and deliver AI-powered learning tools that scale across the world and unlock human potential.
About the Team:
AI is at the core of Quizlet's mission to help learners achieve their goals. We are a group of devoted AI engineers and scientists dedicated to advancing Quizlet’s mission using machine learning, foundation models, and other AI technologies. We are building the key pillars of an AI-powered learning platform, including a comprehensive Learning Knowledge Graph and utilizing the state-of-the art foundation model, to make Quizlet the "Spotify for Learning." Our work is central to making education more effective, engaging, and personalized for our millions of users worldwide.
About the Role:
As a Principal AI Engineer, you will be a key individual contributor, leading the technical vision and development that will define the future of AI in education. This role is about more than just building models; it’s about architecting a cohesive AI ecosystem that breaks down existing silos and delivers truly personalized learning experiences. You will tackle some of our biggest challenges, from fending off competition from large, general-purpose LLMs to transforming our vast content library into a deeply understood and discoverable asset. You will develop novel techniques to personalize study materials, understand user learning patterns, establish pedagogical benchmarks, and optimize the entire AI pipeline from training to serving.
We’re happy to share that this is an onsite position in our San Francisco office. To help foster team collaboration, we require that employees be in the office a minimum of three days per week: Monday, Wednesday, and Thursday and as needed by your manager or the company. We believe that this working environment facilitates increased work efficiency, team partnership, and supports growth as an employee and organization.

In this role, you will:

• Lead the architecture and development of Quizlet’s Learning Knowledge Graph, using unsupervised representation learning and entity linking techniques to model the relationships between millions of learners and study concepts
• Design and deploy next-generation semantic search and retrieval-augmented generation (RAG) systems to dramatically improve the relevance and quality of content discovery
• Drive the strategy and execution of identifying and developing learning foundation models, guiding the transition from leveraging external LLMs to building Quizlet-specific multimodal models that can power a truly personalized AI tutor
• Establish an industry-defining benchmark and evaluation framework to rigorously measure the pedagogical effectiveness of our learning tools and guide future model development
• Build and scale robust, state-of-the-art MLOps pipelines to support rapid experimentation and deployment of AI features, ensuring our infrastructure is both powerful and efficient
• Mentor and guide other engineers on the team, setting the technical standard for AI development and fostering a culture of innovation and research

What you bring to the table:

• 8+ years of experience applying AI research to build real-world products in both industrial and academic environments
• A Ph.D. in Computer Science, Machine Learning, Natural Language Processing, or a related field
• A proven track record of leading high-impact projects and publishing in top-tier ML/NLP conferences (e.g., NeurIPS, ICML, ACL, EMNLP)
• Deep technical expertise in pre-training and fine-tuning large language models, retrieval-augmented generation, and unsupervised representation learning
• Extensive experience building and deploying scalable, high-performance ML systems that have served millions of users
• A strong foundation in software engineering principles and proficiency in languages like Python and C++, and libraries like PyTorch or TensorFlow

Bonus points if you have:

• A background in creating sophisticated LLM agents that can perform multi-step reasoning and research
• Experience in advanced NLP tasks such as entity linking, coreference resolution, and question answering
• A passion for open-source projects and a history of contributing to the AI community.