Principal Systems Engineer (£150k-£195k + Equity) at Harmonic Security Inc.

About the job 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 Principal Systems Engineer Salary £150k-£195k + Equity Company Description Harmonic Security Inc. is a ~$25M Series A cybersecurity startup backed by Next47 and Ten Eleven Ventures, defining the AI security category. They build zero-touch data protection platforms that allow enterprises to safely adopt AI tools by protecting sensitive data at the endpoint in real time with sub-500ms inference. Job Description As a Principal Systems Engineer at Harmonic Security Inc., you will lead the development of low-level, security-critical endpoint agent software. Operating across Windows, macOS, and Linux, you’ll build high-performance Rust components that monitor and protect data movement. This is a mission-critical role defining how enterprises secure their AI-driven future at the OS level. Location London, UK Why this role is remarkable Build a category-defining product at a $25M Series A startup founded by seasoned cybersecurity leaders who previously built Digital Shadows. Work at the cutting edge of AI-first security, writing high-performance Rust code that runs on millions of devices with sub-500ms latency. High-impact leadership role reporting to the VP of Engineering, influencing the core architecture and technical direction of the entire endpoint platform. What You Will Do Design and optimize security-critical endpoint agent components in Rust, ensuring reliability across Windows, macOS, and Linux platforms. Architect foundational agent systems for signal collection and on-device controls, setting the technical bar for correctness, performance, and safety. Work closely with backend and security engineers to bridge low-level system signals with enterprise-grade policy enforcement and real-time observability. The ideal candidate Strong production experience in Rust or C++, with a deep understanding of memory safety, concurrency, and systems programming fundamentals. Proven track record building security-critical client software like EDR, XDR, or DLP agents across multiple operating systems. A proactive, AI-first mindset, comfortable using tools like Cursor or Claude to accelerate development and solve complex, low-level technical challenges. 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.