Principal Machine Learning Engineer - League of Legends

At Riot, we are investing into League of Legends to grow our beloved game for generations to come. With Summoner’s Rift, ARAM Mayhem, and plenty of other gameplay experiences in the works, we are focused on improving our new player experience across many vectors, including our Bots. We want players to be able to learn how to play in fun, dynamic environments in which human-like Bots surprise, delight, and challenge them to learn the game.

As a Principal Machine Learning Engineer, you will unlock better Bots for League of Legends at a pivotal time in the game’s history. You will be forming and testing various ML and AI approaches to training bots that can play with and against human players of varying skill and experience levels. This is a key area of our product strategy and you will be at the forefront of us improving the player experience for millions of players across the globe. Reporting directly into the game team, you will collaborate with game engineers, UX designers, and Insights analysts to test, optimize, and deploy your bot approaches utilizing live data and experimentation. You could also be involved in building a variety of ML applications for League including but not limited to content generation, artist tools, and design tools.

Responsibilities:

• Lead the modeling strategy for AI Bots on League of Legends, focusing on training agents that can understand game state, make decisions, and create compelling player experiences across a variety of game modes and skill levels.
• Develop predictive features and signals from gameplay telemetry, unstructured game data, and simulation outputs, ensuring quality, interpretability, and reliability.
• Design and implement ML systems using methods including reinforcement learning and imitation learning, on-/off-policy algorithms, policy gradient methods, behavior shaping, and hybrid systems that combine learned policies with rule-based or scripted components.
• Define evaluation frameworks for game AI that balance generalizable approaches with genre-specific metrics, adapting methods for the needs of each game mode.
• Ensure the safety, fairness, and trustworthiness of autonomous agents operating in live player environments.
• Collaborate with game and platform engineers, along with UX teams, to integrate models into production in ways that enhance player experience and maintain operational reliability.
• Contribute to the AI community at Riot, sharing methods and learnings with other MLEs across the company.

Required Qualifications:

• Extensive experience (8+ years) delivering ML systems in production, including reinforcement learning, imitation learning, or simulation-based training in rich, interactive environments such as game worlds or multi-agent simulations.
• Proven ability to design modeling strategies and architectures adopted across multiple games or interactive products.
• Expertise working with gameplay telemetry, simulation data, or other complex interactive environments for feature engineering and training.
• Game engineering/C++ experience to write telemetry hooks is a plus.
• Strong track record building and optimizing agent-based systems or world models for dynamic, player-facing environments.
• Hands-on experience with relevant ML methods including reinforcement learning and imitation learning (such as behavior cloning and inverse reinforcement learning), on-/off-policy algorithms, policy gradient methods, behavior shaping, and hybrid systems that combine learned policies with rule-based or scripted components.
• Mastery of experiment design, model evaluation, and optimization for autonomous agents.
• Track record of incorporating human considerations into AI applications, such as responsible AI safety and UX best practices.
• League of Legends game context and/or demonstrated ability to learn competitive game systems at a rapid rate..
• Familiarity with integrating ML-driven agents into live game environments with game and platform engineers.

For this role, you'll find success through craft expertise, a collaborative spirit, and decision-making that prioritizes the delight of players. We will be looking at your past studies, experience, and your personal relationship with games. If you embody player empathy and care about players' experiences, this could be your role!

Our Perks:

Riot focuses on work/life balance, sh