Callosum develops system-level software that allows different AI chip architectures to interoperate, enabling flexible, sovereign AI infrastructure.
ABOUT US The last era of AI scaled on a single bet: bigger models, more identical chips, more data. As problems grow more complex and the requirements of intelligence more diverse, that bet is breaking down. Real-world problems are heterogeneous: no single model or chip can solve them alone. The next era of AI requires heterogeneity at the infrastructure level - diverse models on diverse chips, each with distinct strengths, co-evolving into systems of capability that move the Pareto frontier of what is possible. That's what we are building. Callosum is the Intelligent Systems Company. We started from questioning what actually creates intelligence. We believe there is no single answer, but rather a system-level solution. We co-evolve models, workflows, and silicon together to show that intelligence does not come from a single component, but it emerges from the diversity of co-optimised mechanisms working together and aware of each other. Heterogeneity will define the next era of compute, and is a principle that holds in biological, neuronal, and economic systems alike. In early 2026 we launched with results showing orders of magnitude improvements in performance, and this is only the beginning. Agentic AI is the future of how intelligence is deployed: multi-step, long-horizon, and operating in changing environments. These systems are inherently heterogeneous, and can only be as powerful as the infrastructure that runs them. We are engineers and scientists based in London, working together 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. ABOUT THE ROLE The Applied AI team own Callosum's customer engagements end to end. You will work directly with customer engineering teams to understand their AI workloads, design and run rigorous evaluations against their production pipelines, integrate optimised workflows into their systems, and make sure the results hold in production. At Callosum, Applied AI Engineers are the technical bridge between what customers run and what we build. What you learn shapes the research and platform roadmap. The evaluations you run are how we prove the technology in production. As an early member of the team, you will help build the methodology, tooling, and engagement practices the function runs on. The role is engineering-led: you will employ technical judgment to recognise what kind of system a problem needs and prototype it. You will work closely with the engineers designing new intelligent systems, with the platform team that serves them, and directly with senior technical stakeholders on the customer side. We run a flat Member of Technical Staff structure. Responsibility and scope grow with what you demonstrate, including leadership of the Applied AI function as the team scales. WHAT YOU'LL BUILD - Customer engagement from first workload scoping through evaluation, integration, and production deployment - Design and run rigorous evaluations on customers' production workloads: set success criteria, instrument the comparison, present results to their engineering teams - Develop deep technical understanding of customer systems (retrieval pipelines, agentic workflows, code intelligence stacks) and design optimised Callosum workflows - Integrate Callosum workflows into customer environments and support them through to stable production - Work with our research and platform teams to turn what you learn into general product capability - Build the team's shared methodology: evaluation harnesses, integration runbooks, and engagement standards WHAT YOU BRING - Exceptional technical depth, demonstrated through any of: production systems at scale, research that shipped, or an early/founding role where you owned the system end to end - Experience with LLM serving infrastructure, agent orchestration, or retrieval systems - Rigour in evaluation or benchmarking work - A bias for action, comfort with ambiguity and a strong sense of ownership WHAT SETS YOU APART - Experience working directly with external engineering teams, whether as a forward deployed engineer, solutions architect, technical consultant, or comparable customer-facing role - Familiarity with novel accelerator platforms - Experience at an early-stage company or in a founding-engineer role WHAT WE OFFER - 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.