Head of Physical Infrastructure

📋 Job Overview

We’re living through a Cambrian explosion of intelligence: new models and new chips, each specialised for different tasks, are arriving all at once. The result is a new era for AI, one of radical heterogeneity. Callosum is the Intelligent Systems Company. We believe the next generation of AI won't be defined by any single model or chip, but by intelligent systems in which hardware and intelligence co-evolve. We are building the infrastructure that unifies heterogeneous compute across the full stack. This opens a new axis of scaling intelligence: a dynamic system that tailors itself to what each workload actually needs, whether that's speed, cost, precision, or whatever unit comes next.

🏢 About Callosum

Callosum is the Intelligent Systems Company. We believe the next generation of AI won't be defined by any single model or chip, but by intelligent systems in which hardware and intelligence co-evolve. We are building the infrastructure that unifies heterogeneous compute across the full stack. This opens a new axis of scaling intelligence: a dynamic system that tailors itself to what each workload actually needs, whether that's speed, cost, precision, or whatever unit comes next. We are engineers and scientists based in London, working across the full depth of the stack. We are curious, intellectually honest, and building what doesn't exist yet. If you thrive on uncharted territory and are energised by the scale of the challenge, we'd love to hear from you.

🎯 The Role

Callosum believes that the next generation of AI infrastructure will be built from a much more diverse set of hardware than the clusters of today. Scaling that infrastructure creates a new physical systems problem: different accelerators bring different power densities, cooling requirements, rack constraints, network topologies, vendor dependencies, and deployment models. We want to find ways to turn those increasingly complex inputs into physical infrastructure that can be deployed repeatedly and scaled. This role owns Callosum’s physical compute infrastructure, from the first assessment of a potential deployment through to the reliable operation of the resulting cluster. You will scope sites, coordinate the design cluster infrastructure and deployment across vendors and facilities, and lead commissioning of new hardware. As our footprint grows, you will build and lead the team responsible for keeping that infrastructure healthy, observable, and available, establishing the operational systems that turn individual deployments into a reliable fleet.

✅ Key Responsibilities

• Scope new cluster deployments across site selection, power, cooling, rack layout, networking, storage, fibre connectivity, and capacity requirements
• Coordinate delivery and commissioning across facilities, utilities, OEMs, networking and storage vendors, ensuring the physical and technical dependencies come together
• Build the operational infrastructure for the fleet, including hardware telemetry, health monitoring, maintenance, incident response, capacity planning, and hardware lifecycle management
• Build and lead the physical infrastructure team responsible for deploying new clusters and maintaining the reliability and availability of the resources we operate

📌 Required Qualifications

• Experience designing, deploying, or operating high-density compute infrastructure, HPC clusters, AI infrastructure, or similarly complex physical systems
• Strong understanding of how power, cooling, rack design, networking, storage, and compute interact to determine the capabilities and constraints of a cluster
• Demonstrated ability to drive complex infrastructure deployments across technical teams, facilities, hardware vendors, network providers, and other external stakeholders
• Experience building and leading infrastructure teams, with strong operational instincts around reliability, observability, capacity, maintenance, and failure management

🎁 Benefits

• Competitive Salary, determined by skills and experience
• Equity & Ownership
• Private healthcare
• We offer Visa sponsorship and relocation benefits to hire the best in the world
• We work in person at our London office. You'll have the tools, space and setup to do your best work, and if you have specific needs, just tell us
• We're committed to building an inclusive workplace where everyone feels welcome, and believe in equal opportunities for all.

🛂 Visa & Eligibility

• We offer Visa sponsorship and relocation benefits to hire the best in the world