RL Research Engineer (Up to £350k + Equity) at well-funded cybersecurity AI startup

This is a job that Jill, our AI Recruiter, is recruiting for on behalf of one of our customers. She will pick the best candidates from Jack's network. The next step is to speak to Jack. \=\=\= Job Title RL Research Engineer Salary Up to £350k (Including Equity) Company Description Well-funded cybersecurity AI startup Job Description As an RL Research Engineer, you will own the post-training pipeline for specialist language models that detect security threats in real-time. You will design and ship RL pipelines—including RLHF, DPO, and GRPO—to classify malicious trajectories. Your work ensures autonomous systems are resilient against adaptive attacks, providing critical security infrastructure for enterprise AI. Location London, UK Why this role is remarkable * Join a high-pedigree founding team building mission-critical defense infrastructure for the next generation of autonomous AI systems. * Backed by top-tier VCs, this seed-stage startup addresses the urgent need for adaptive security in an increasingly agent-led threat landscape. * Take significant ownership as you shape the core detection logic and training infrastructure for a highly technical, high-impact product. What You Will Do * Design and ship RL post-training pipelines such as RLHF, DPO, and GRPO to optimize models for real-time security threat classification. * Build and maintain scalable training infrastructure end-to-end, including distributed training, evaluation harnesses, and rigorous regression testing. * Develop custom reward models and preference optimization systems tailored to identifying complex, long-horizon malicious agent trajectories. The ideal candidate * Proven hands-on experience with RL post-training for language models (RLHF, DPO, or similar) in a production or research setting. * Strong engineering fundamentals with the ability to operate complex training pipelines at scale using PyTorch, JAX, and distributed computing. * A background in machine learning research, ideally with a PhD or equivalent expertise in optimization, alignment, or reinforcement learning. \=\=\= Who are Jack \& Jill? Ok, I'll go first. I'm Jack, an AI that gets to know you on a quick call, learning what you're great at and what you want from your career. Then I help you land your dream job by finding unmissable opportunities as they come up, supporting you with applications, interview prep, and moral support. And I'm Jill, an AI Recruiter who talks to companies to understand who they're looking to hire. Then I recruit from Jack's network, making an introduction when I spot an excellent candidate. How does this work? * Jack's an AI agent for job searching and career coaching. He works for you. * Jill is the AI recruiter working for the company. She recruits from Jack's network. * If it's a match and the company wants to meet you, they'll make the intro. In the meantime, if you'd like, Jack will send you excellent alternatives. We never post fake jobs This isn't a trick. This is an open role that Jill is currently recruiting for from Jack's network. Sometimes Jill's clients ask her to anonymize their jobs when she advertises them, which means she can't share all the details in the job description. We appreciate this can make them look a bit suspect, but there isn't much we can do about it. Give Jack a spin! You could land this role. If not, most people find him incredibly helpful with their job search, and we're giving his services away for free.