About Us

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.

The last era scaled on a different bet: one bigger model, more of the same chip, more data. That bet is running into structural limits. Frontier models offer extraordinary capability at unsustainable cost, one that today's monolithic infrastructure was never designed to serve.

Our founding principle is that intelligence comes from many specialised systems working together, not from any single component. We build the software orchestration layer that co-evolves models, workflows and silicon into one system, delivering inference tailored to every workload, and demonstrating orders-of-magnitude leaps in capability and cost.

Because our software spans the full stack, our engineering team works directly with heterogeneous accelerators and frontier silicon, including Cerebras, d-Matrix, Intel, NVIDIA, AMD, Normal Computing, Tenstorrent, GreatSky, and Mixx. We are not stopping at today's chips: each new generation of silicon unlocks algorithms that couldn't run before, and we intend to be first to them, every time. If we get it right, it will belong to everyone building on it - not to any single vendor.

In our latest funding round, we raised $100M, led by Atomico with participation from Plural, DCVC and the UK Sovereign AI Fund’s first investment. With this, we are building the infrastructure for the next era of intelligence.

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.

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.