Product Engineer (Backend)

White Circle; Paris; Hybrid; EUR 80,000 - 178,000; Full time

Benefits offered by this job

Equity

Relocation package

Hybrid work (Paris)

Medical insurance (France)

Equipment provided

AI tools subscriptions

Team off-sites

Job summary

White Circle is seeking a Product Engineer (Backend – Rust) to own and evolve core systems powering AI safety at scale—building APIs that handle hundreds of millions of requests with low latency and high reliability.

You will design and ship backend services in Rust, own features end-to-end from API design to database schema and deployment, and collaborate with product and research to turn requirements into production systems. Paris-based hybrid role with relocation.

Qualifications

• Backend systems experience in Rust or similar
• Async Rust (Tokio) proficiency
• Familiarity with Axum/Actix or similar
• Strong PostgreSQL knowledge and query optimization
• Understanding of distributed systems and scaling
• Experience designing APIs and schemas
• Ability to monitor and improve performance
• Knowledge of caching and observability
• Clear communication and collaboration
• Experience with Python or Go is a plus

Responsibilities

• Design and build backend services in Rust with real-time policy checks at scale
• Own features end-to-end from API design to database schema to deployment
• Work across the stack when needed to solve problems
• Improve system performance and reliability (connection pooling, caching, queries)
• Collaborate with product and research to translate requirements into production systems

Skills

Rust backend

Async Rust (Tokio)

Rust web frameworks

PostgreSQL

Distributed systems

API design

Performance optimization

Caching

Observability

Python/Go

Tools

ClickHouse

Redis

Kafka

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

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

• Salary of $90,000 to $200,000 + equity

• 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

1. Intro call with one of our colleagues

2. Show your best during the technical interview

3. Final call with our CEO and Head of Engineering