Riot has petabytes of data and state-of-the-art processing technologies to build products that elevate the player experience at a massive scale.

As a Sr. Principal ML Engineer within the Central Product team, you will define and drive the modeling architecture that powers personalization, matchmaking, and social experiences across the player ecosystem - in and around the game.Working alongside Product Leaders, Software Engineers & Data Engineers who lead foundational data systems for social graph, presence, chat, and matchmaking telemetry, you will lead the AI and modeling layer that transforms this data into intelligent, adaptive, and fair experiences for our players. 

Your work ensures that every player connection - from friend recommendations to lobby matchmaking and in-game social features - feels meaningful, fair, and personalized through responsible, scalable machine learning systems.

Responsibilities:

• Modeling Architecture for Player Intelligence Graph

  • Define and lead the modeling architecture that powers player personalization, matchmaking, social graph recommendations, and community discovery.
  • Develop models for churn model, revival models.
  • Drive multi-objective optimization frameworks balancing fairness, latency, diversity, and experience quality.
  • Establish and standardize evaluation protocols (match quality, satisfaction metrics, toxicity mitigation).
• Real-Time Lifecycle, Personalization & Player Experience AI
  • Build real-time inference systems for personalized content, store offers, matchmaking and player interactions at scale.
  • Partner with the Data Engineers to integrate low-latency data pipelines and feature stores into online model serving.
  • Lead adoption of contextual bandits, reinforcement learning, and graph ML for adaptive, session-aware personalization.
  • Drive experimentation systems for live-service optimization (player retention, engagement, satisfaction).
• Collaboration & Cross-Disciplinary Influence
  • Work in lockstep with the Product leaders, Software Engineers & Data Engineers to define data schema, pipeline, and feature requirements that support advanced modeling.
  • Collaborate deeply with Data Engineers to align ML and data-system architecture.
  • Co-define standards for data schema design, feature lineage, and model observability.
  • Jointly drive automation and reliability across the data + ML lifecycle — from ingestion to inference.
  • Ensure shared governance for real-time player data, ensuring quality, security, and compliance.
• AI Governance
  • Define Responsible AI standards for matchmaking and social systems — including fairness, transparency, and explainability.
  • Implement bias mitigation and trust calibration mechanisms to ensure equitable player experiences.
  • Partner with Research and Player Dynamics teams to ensure ethical alignment and reduce emergent negative behaviors.
  • Lead post-launch evaluations of algorithmic impact on community health and player sentiment.

• System Architecture & Optimization

  • Drive org-wide model optimization standards - latency, throughput, memory efficiency.
  • Architect systems for multi-model orchestration (e.g., skill, preference, and toxicity models working in concert).
  • Define telemetry standards for online model observability and drift detection.
  • Partner with platform teams to optimize inference cost and hardware utilization.
• Mentorship & Cross-Disciplinary Leadership
  • Mentor senior ML engineers and data scientists, strengthening system design and experimentation practices.
  • Collaborate with Data Engineering, Game Engineering, and Player Insights teams to define unified data contracts.
  • Represent the ML discipline in cross-functional design reviews, ensuring data-driven decision making.
  • Contribute to hiring, interview calibration, and craft council development for ML excellence.

Required Qualifications: 

• 15+ years in Machine Learning or Applied AI; 3+ years in a principal or staff-level technical leadership role.
• Proven experience in real-time, large-scale ML systems - matchmaking, recommendations, or personalization.
• Deep expertise in graph ML, reinforcement learning, and representation learning.
• Proficiency in PyTorch, TensorFlow, JAX, and modern data/serving frameworks (Ray, Kafka, Flink, Redis).
• Strong understanding of A/B testing, experiment design, and player experience metrics.
• Track record of defining cross-team ML standards and leading technical direction.

Desired Qualifications:

• Background in game development, player behavior modeling, or social ecosystems.
• Experience in trust & safety, toxicity detection, or community health models.
• Familiarity with Vertex AI, SageMaker, or internal orchestration systems for real-time inference.
• Demonstrated success integrating ML systems with live-service game backends.

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, shown by our open paid time off policy and other perks such as flexible work schedules. We offer medical, dental, and life insurance, parental leave for you, your spouse/domestic partner, and children, and a 401k with company match. Check out our benefits pages for more information.

At Riot Games, we put players first. That mission drives every decision in our quest to create games and experiences that make it better to be a player. Whether you’re working directly on a new player-facing experience or you’re supporting the company as a whole, everyone at Riot is part of our mission. And just like in our games, we’re better when we work together. Our goal is to create collaborative teams where you are empowered to bring your unique perspective everyday. If that sounds like the kind of place you want to work, we’re looking forward to your application.

It’s our policy to provide equal employment opportunity for all applicants and members of Riot Games, Inc. Riot Games makes reasonable accommodations for handicapped and disabled Rioters and does not unlawfully discriminate on the basis of race, color, religion, sex, sexual orientation, gender identity or expression, national origin, age, handicap, veteran status, marital status, criminal history, or any other category protected by applicable federal and state law. We consider for employment all qualified applicants, including those with criminal histories, in a manner consistent with applicable federal, state and local law, including the California Fair Chance Act, the City of Los Angeles Fair Chance Initiative for Hiring Ordinance, the Los Angeles County Fair Chance Ordinance for Employers, the San Francisco Fair Chance Ordinance, and the Washington Fair Chance Act.

Per the Los Angeles County Fair Chance Ordinance, the following core duties may create a basis for disqualifying candidates with relevant criminal histories:

• Safeguarding confidential and sensitive Company data
• Communication with others, including Rioters and third parties such as vendors, and/or players, including minors
• Accessing Company assets, secure digital systems, and networks
• Ensuring a safe interactive environment for players and other Rioters

These duties are directly related to essential operations, safety, trust, and compliance obligations within our organization. Please note that job duties may evolve based on business needs and additional responsibilities may be assigned as necessary to maintain operational efficiency and security.