Principal Software Engineer - Networking

What You'll Do As a Principal Software Engineer - Networking, you will help set the technical direction for Radiant's networking software, and lead the design and delivery of the systems that build, automate, and operate the fabric connecting our GPU clusters. You'll work across high-performance cluster fabrics, network automation, Managed Networks, and multi-tenant isolation. You'll partner closely with product, infrastructure, SRE, storage, and security teams, and with customers whose workloads depend on the network. This is a hands-on technical leadership role focused on making our networks fast, reliable, and fully software-driven, through architecture, code, and the standards other teams build on. Key Responsibilities Set the technical vision and architecture for Radiant's networking software, and lead its design and implementation. Design and build the control plane that provisions, configures, and automates our cluster fabrics and Managed Networks. Translate product and customer requirements into robust architectures, APIs, and technical designs, working closely with Product. Own network performance, isolation, and reliability for AI training and inference workloads. Lead integration of networking with compute, Kubernetes, storage, security, and observability. Drive operational excellence with SRE and Infra Ops, including automation, monitoring, and incident response. Raise the engineering bar across the organisation through mentoring, design and code review, and technical standards. Your Profile Extensive experience building and operating large-scale network software or software-driven networks. A track record of technical leadership at staff or principal level, including setting direction across multiple teams and delivering complex, high-stakes systems. Strong hands-on engineering skills in one or more systems languages such as Go or similar. Deep technical expertise across: Fabrics: RDMA, InfiniBand, RoCE, Ethernet at scale, congestion control Networking: routing, switching, BGP, EVPN/VXLAN, overlays and underlays Automation: network-as-code, configuration management, APIs for network devices Multi-tenancy: isolation, segmentation, network security Hands-on experience with technologies such as NVIDIA networking, SONiC, Cumulus, or similar. Understanding of how network design affects AI training and inference performance. Excellent written and verbal communication, including clear design documents and explaining complex trade-offs to technical and non-technical audiences. Comfortable working directly with customers on highly technical problems. What You Bring Networking domain expertise: Understand how the network shapes workload performance, from the fabric up to the application. Engineering excellence: Write and review code that sets the standard for correctness, performance, and maintainability. Architectural judgement: Make sound long-term decisions on systems that are hard to change once built. Technical leadership: Influence direction across teams without relying on authority, and grow the engineers around you. Systems thinking: Understand how your area interacts with compute, networking, storage, and the rest of the cloud platform. Ownership: Drive capabilities from design through production, operation, and continuous improvement. Qualities we look for: Set the standard: Every single day, you spot opportunities to constructively shake things up Inspire the change: There's no blueprint for the future. You'll embrace challenges and change You're real and you're true to yourself: We cherish and celebrate diversity so you'll feel right at home whoever you are and whoever you're talking to, you treat everyone the same. Why should you join us? What sets us apart is our blend of modern technology, competitive benefits, and an open, welcoming work culture that enables our people to thrive. Here are just some of the great things you can expect from us: 25 days of annual leave A culture that emphasises results over hierarchy, process & ego: we place great emphasis on the quality, ingenuity and creativity of work. Open communication, regular feedback: we value smooth collaboration, direct and actionable feedback, and believe that leading with empathy and a growth mindset makes us better together. Learning Time: we all have dedicated learning time to focus on new skills, projects or interests that lay outside of your day-to-day job. Health & Wellbeing: we want everyone to feel healthy and happy, so we offer private medical insurance via Bupa. Cycle to Work Scheme: we're committed to building a sustainable business, so we encourage cycling to work. Gympass subscription to a variety of gyms and wellbeing apps Participation in the company shares program Enhanced parental pay & leave Our process: Talent screen → Hiring Manager → Technical interview (two Principal Engineers) → Whiteboard Exercise → Final. Company Overview: Radiant is redefining how AI infrastructure is built. We design and operate AI-native cloud platforms engineered for sovereignty, performance, and scale. Our infrastructure powers GPU-native workloads, multi-tenant control planes, and high-performance AI systems designed for the most demanding environments. We are not building a generic cloud. We are building purpose-built AI infrastructure — from powered land, to compute, to software. As we scale, we're building this organisation from the ground up. We're looking for people who'd rather build the playbook than inherit one — who are comfortable doing the work themselves as well as directing others, and who can adapt as fast as our strategy does. This is a startup model: attitude and adaptability matter more to us than years of experience or the size of the team you've previously managed.