Backend Engineer

What You'll Do

• Build API-based products from the ground up. Design and ship low-latency, high-reliability APIs and services that power Leaderboards, Evals, and Arena data products.
• Turn evaluations into product. Partner with the research team to take novel eval methods and make them durable, full-featured products: scoring pipelines, data models, and the APIs that expose them.
• Ship enterprise-grade backends. Usage metering, cost attribution, billing integration, authentication, RBAC, multi-tenancy, and audit logging.
• Own the data architecture. Unify public and private evaluation data, design schemas that hold up as the product grows, and make Arena’s data queryable, consistent, and fast.
• Flex across the stack. Contribute to the backend of our Leaderboards and Evals platforms when needed, helping unify our public and private data architectures.

What We're Looking For

• 5+ years of backend engineering experience, with meaningful time spent on building product-facing APIs, services and data systems at scale.
• Strong proficiency in a modern backend language — Go preferred — and the judgment to design APIs other engineers and customers will live with for years.
• Solid data fundamentals. Comfortable modeling, querying, and scaling Postgres; know when to reach for Redis, a queue, or a warehouse.
• Experience composing services into products — integrating payments, auth, analytics, or data pipelines into something coherent and reliable.
• A product-oriented mindset. Think about the developer experience of your APIs, not just the implementation.
• Comfort with ambiguity. Scope is fluid and you’ll wear many hats.

Nice to Have

• Experience with LLM provider APIs (OpenAI, Anthropic, Google, etc.) and the realities of building on them: streaming, token accounting, rate limits, model-specific quirks.
• Background in ML infrastructure, model serving, or evaluation frameworks.
• Experience building enterprise-ready features: SSO, RBAC, audit logs, multi-tenancy.
• Experience building billing and usage infrastructure around systems like Stripe, Metronome, and Orb.
• Familiarity with the modern AI stack (vLLM, LiteLLM, LangChain, etc.).

What 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.