Product Engineer (Backend)

TLDR: We're looking for a Product Engineer (Backend – Rust) to own and evolve the core systems that power AI safety at scale – building APIs that handle hundreds of millions of requests, real-time policy enforcement, and high-throughput data pipelines. ABOUT US White Circle https://whitecircle.ai is an AI Safety company building the safety, reliability, and optimization layer for AI systems. At the core of our platform are policies – simple natural-language rules that define what an AI model should and shouldn’t do. We automatically test, enforce, and continuously improve these policies at scale. - We’ve recently raised our Series A funding round, taking our total funding to $70M. Our investors include top funds, founders, and senior leaders at OpenAI, Anthropic, HuggingFace, Mistral, DeepMind, Datadog, Sentry, and others - We process over one hundred million API calls every month - We fine-tune and train our own LLMs so they run faster and cheaper than any open or proprietary model We’re a small, highly focused team. If you want to work deeply on hard problems, see your work ship to production quickly, and influence how AI safety is actually built – you’re the one we need. YOU WILL - Design and build backend services in Rust that handle real-time policy checks at scale – low latency, high reliability. - Own features end-to-end: from API design to database schema to deployment. You ship, you monitor, you iterate. - Work across the stack when needed – we care more about solving problems than role boundaries. - Improve system performance and reliability – connection pooling, caching strategies, query optimization, observability. - Collaborate directly with product, research to turn requirements into production systems. YOU’LL FIT RIGHT IN IF YOU - You've built and shipped backend systems in Rust, Python or Go. - You're comfortable with async Rust (Tokio), web frameworks (Axum, Actix), and database access patterns. - You have strong fundamentals in system design – you can reason about trade-offs, failure modes, and scaling. - You've worked with PostgreSQL and know how to write efficient queries, design schemas, and debug performance issues. - You communicate clearly and work well with others. Fluent English. A big plus - Experience with ClickHouse, Redis, or Kafka/event streaming - Experience with LLM infra, including LLM routing, inference systems, and RAG architectures - Background in high-throughput monitoring systems, fintech WHY WHITE CIRCLE - Competitive compensation package, including equity - Flexible time off - Paid time off in line with your local regulations, no matter where you work from - Work from Paris (hybrid) + relocation package - Best medical insurance in France - Learning and development support for courses, conferences, and opportunities to grow your skills - All the hardware, tools, and services you need - Covered subscriptions for AI agents and IDEs - Team off-sites twice a year: we’ve recently been to the Alps and to Saint-Tropez PROCESS 1. Intro call with Talent 2. Technical interview 3. Final call with CEO and Head of Engineering