Product Engineer (Backend)
Whitecircle · Paris
What this role requires
2 requirements, read out of the advert rather than guessed from the job title:
Also mentioned, not required: Python, Go, Tokio, Axum, Actix, ClickHouse, Redis, Kafka. Worth having, but their absence is not what gets a CV filtered out.
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Job description
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
Read the full description (31 more sections)Show less
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
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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