Senior ML Engineer

Castle ( https://castle.io ) | Senior ML Engineer | Senior R&D Detection Engineer | REMOTE (Europe/EMEA) | Full-time Hi HN! I’m Antoine, Head of Research at Castle. We’re a YC-backed Series A startup helping companies like Canva, Atlassian, and Rockstar Games fight fraud and abuse. We're building modern, AI-powered bot detection and abuse prevention tech, with a focus on real-time protection and behavioral intelligence. We’re a small, fast-moving team looking to add two technical roles: Senior ML Engineer – Fraud & Bot Detection You'll work on real-time ML pipelines, anomaly detection, and adversarial ML techniques to stop bots and malicious actors. We’re combining traditional fraud signals with modern AI—LLMs, behavioral clustering, and vector-based search—to stay ahead of attackers. You’ll own models end to end and deploy quickly, with direct access to rich, structured behavioral and fingerprinting data. Ideal for someone with strong experience in the anti-fraud/anti-bot field who loves cutting-edge ML and wants immediate impact. Senior Detection Engine Engineer (R&D) You’ll build and scale the core infrastructure behind our detection logic—rule engines, fingerprinting pipelines, and high-speed signal ingestion. We’re integrating AI-driven detection and auto-adaptive logic that reacts in real time. If you enjoy real-time systems, security, and automation, this is a highly technical role that’s at the core of our detection stack. Perfect if you’ve worked in security, data pipelines, or real-time analytics and want to outsmart fraudsters. We pay US salaries globally | Fully remote from Europe/EMEA timezone | Flexible hours | Unlimited PTO | Paid parental leave We're actively hiring and committed to responding to every qualified applicant. Drop us a line: antoine.vastel@castle.io