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

• 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.