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 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
• Intro call with one of our colleagues
• Show your best during the technical interview
• Final call with our CEO and Head of Engineering Please submit your application in English.