Senior Infrastructure Engineer

About LMArena

LMArena is the open platform for evaluating how AI models perform in the real world. Created by researchers from UC Berkeley’s SkyLab, our mission is to measure and advance the frontier of AI for real-world use.

Millions of people use LMArena each month to explore how frontier systems perform — and we use our community’s feedback to build transparent, rigorous, and human-centered model evaluations. Leading enterprises and AI labs rely on our evaluations to understand real-world reliability, alignment, and impact. Our leaderboards are the gold standard for AI performance — trusted by leaders across the AI community and shaping the global conversation on model reliability and progress.

We’re a team of researchers, engineers, academics, and builders from places like UC Berkeley, Google, Stanford, DeepMind, and Discord. We seek truth, move fast, and value craftsmanship, curiosity, and impact over hierarchy. We’re building a company where thoughtful, curious people from all backgrounds can do their best work. Everyone on our team is a deep expert in their field — our office radiates excellence, energy, and focus.

About the Role

LMArena is seeking a Senior Infrastructure Engineer to define, build, and evolve the technical foundations that power the world’s most transparent AI evaluation platform. This is not just an architecture role - you’ll partner directly with product, security, and data teams to identify bottlenecks, design resilient systems, and ship the code that keeps our platform fast, reliable, and secure at scale.

You’ll have a broad impact across the stack : optimizing performance, building primitives that accelerate feature delivery, hardening our systems against abuse, and scaling infrastructure to handle billions of API requests and real-time votes. If you love working across boundaries, getting deep into code, and making infrastructure a product in its own right, this is the role for you.

You’ll

Own technical strategy for LMArena’s core infrastructure - networking, APIs, services, data systems, and security foundations.

Design and implement high-performance systems that scale to hundreds of millions of real-time interactions and evaluations per day.

Collaborate with security engineering to embed anti-abuse measures, Sybil resistance, and trust systems into core platform architecture.

Partner with product engineering to deliver infrastructure improvements that directly accelerate feature velocity and reliability.

Build developer-facing primitives and tooling—internal APIs, SDKs, CI / CD enhancements—that make our platform more productive and safe to build on.

Monitor, profile, and optimize system performance across backend services, databases, and networking layers.

Drive operational excellence through observability, capacity planning, and incident response best practices.

Mentor engineers across the company in building scalable, performant, and secure systems.

You’ll have

8+ years of experience in backend, infrastructure, or systems engineering, including staff-level scope in a high-scale production environment.

Proven experience designing and operating distributed systems at scale (millions of DAU / billions of requests).

Deep knowledge of networking fundamentals, service-to-service communication, and traffic routing at scale.

Hands-on experience with performance profiling, observability, and reliability engineering.

Track record of collaborating with security and product engineering to deliver both foundational systems and user-facing features.

Clear communicator who can lead technical discussions, build alignment across teams, and partner with us to prioritize the needs of the business.

Bonus Points

Experience with Node.js, Typescript, Serverless Environments, Postgres

Background in anti-abuse systems, security engineering, or trust & safety platforms.

Experience building infrastructure for real-time, user-driven platforms.

What we offer

We offer competitive compensation and equity aligned to the markets where our team members are based. The base salary range will depend on the candidate’s permanent work location.

Comprehensive health and wellness benefits, including medical, dental, vision, and additional support programs.

The opportunity to work on cutting-edge AI with a small, mission-driven team

A culture that values transparency, trust, and community impact

Come help build the space where anyone can explore and help shape the future of AI.

LMArena provides equal employment opportunities (EEO) to all employees and applicants for employment without regard to race, color, religion, sex, national origin, age, disability, genetics, sexual orientation, gender identity, or gender expression. We are committed to a diverse and inclusive workforce and welcome people from all backgrounds, experiences, perspectives, and abilities.

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