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 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 raised $11M from 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, and ML teams to turn requirements into production systems. You’ll fit right in if you: You've built and shipped backend systems in Rust – not just tutorials, real production services. 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 Kubernetes and infrastructure-as-code (Terraform, Helm) Background in high-throughput systems monitoring systems, fintech Why White Circle Salary of $80,000 to $150,000 + equity 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 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 How we hire Intro call with one of our colleagues Complete the take-home exercise Show your best during the technical interview Final call with our CEO and CTO Please submit your application in English - it’s our company language so you’ll be speaking lots of it if you join