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.
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We’ve raised $11M from top funds, founders, and senior leaders at OpenAI, Anthropic, HuggingFace, Mistral, DeepMind, Datadog, Sentry, and others
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We process over one hundred million API calls every month
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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:
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Design and build backend services in Rust that handle real-time policy checks at scale – low latency, high reliability.
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Own features end-to-end: from API design to database schema to deployment. You ship, you monitor, you iterate.
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Work across the stack when needed – we care more about solving problems than role boundaries.
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Improve system performance and reliability – connection pooling, caching strategies, query optimization, observability.
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Collaborate directly with product, research to turn requirements into production systems.
You’ll fit right in if you:
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You've built and shipped backend systems in Rust, Python or Go.
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You're comfortable with async Rust (Tokio), web frameworks (Axum, Actix), and database access patterns.
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You have strong fundamentals in system design – you can reason about trade-offs, failure modes, and scaling.
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You've worked with PostgreSQL and know how to write efficient queries, design schemas, and debug performance issues.
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You communicate clearly and work well with others. Fluent English.
A big plus:
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Experience with ClickHouse, Redis, or Kafka/event streaming
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Experience with LLM infra, including LLM routing, inference systems, and RAG architectures
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Background in high-throughput monitoring systems, fintech
Why White Circle
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Meaningful equity package
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Paid time off in line with your local regulations, no matter where you work from
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Work from Paris (hybrid) + relocation package
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Best medical insurance in France
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All the hardware, tools, and services you need
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Covered subscriptions for AI agents and IDEs
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Team off-sites twice a year: we’ve recently been to the Alps and to Saint-Tropez
How we hire
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Intro call with one of our colleagues
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Show your best during the technical interview
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Final call with our CEO and Head of Engineering
Please submit your application in English.
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