White Circle
Product Engineer (Backend)
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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.
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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.
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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
- Meaningful equity package
- 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
- Show your best during the technical interview
- Final call with our CEO and Head of Engineering
Please submit your application in English.
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Jessica, London
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