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 Callosum believes that orders of magnitude improvements in AI systems will come through application-aware orchestration across heterogeneous hardware. We are building that vision: infrastructure that treats the full landscape of compute as a unified, co-evolving system, evolved beyond GPUs. This role owns the developer experience of Callosum's stack, turning complex, low-level systems into something observable, debuggable, and usable by the rest of the team. You'll build the profiling, tracing, and developer tooling that defines how engineers interact with heterogeneous systems, enabling fast experimentation with new accelerators and complex inference workflows. You will own the abstractions, CLIs, and instrumentation that the engineering organisation is built on - primitives that don't yet exist for the next generation of compute infrastructure. As multi-stage and multi-agent workflows grow in complexity, your work is what keeps execution paths visible and tractable, ensuring the organisation can scale without losing insight or control. What You’ll Build * Extend profiling and tracing tooling for new accelerators, including collection, compression, and visualisation of performance data * Develop CLI tools and automation wrappers that simplify common workflows - spinning up inference stacks, launching benchmarks, managing configurations * Converting prototypes of internal tooling into high-performance, scalable, accessible commands * Build tooling to support multi-agent serving workflows: request tracing across agent boundaries, pipeline visualisation, and debugging tools for complex inference DAGs * Create internal libraries and abstractions that let other teams move faster without reinventing shared infrastructure What Sets You Apart * Strong software engineering fundamentals: clean APIs, good error handling, sensible defaults, and clear documentation * Experience with profiling and tracing systems (perf, Nsight, Tracy, or similar) and a good sense of how to make trace data actionable rather than overwhelming * Familiarity with observability stacks (Prometheus, Grafana, OpenTelemetry, or equivalent) in varied infrastructure environments * Comfortable across the stack - from low-level trace collection to dashboards and developer-facing CLI tools 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.