Product Engineer (Backend)

Team: Engineering team Location: Paris Employment type: FullTime

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.