London, United Kingdom
You apply directly with the employer. We never charge applicants.
£158K–£358K/yr
Estimate — the employer hasn't published pay.
Based on 11 similar staff/principal Software Engineering jobs in United Kingdom that show pay. The range is the middle half of their posted pay (25th to 75th percentile), not an offer — ask the employer for the real range.
Software Engineering salaries →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. As workloads become increasingly disaggregated, the performance of the system is determined not only by where computation happens, but by how efficiently state and data can move between the hardware best suited to each part of the workload. Communication latency sets the boundary on how far that disaggregation can go.
This role owns that boundary. You will develop the communication systems that allow heterogeneous accelerators to operate as parts of one system, working across protocols, memory movement, networking hardware, and the software layers above them. That means understanding where overhead actually comes from, removing assumptions inherited from more general-purpose workloads, and finding new ways to move data directly and efficiently across vendor boundaries. The remit is intentionally broad: from RDMA paths and programmable NICs to cache transfer formats and emerging interconnect technologies, you will own the technical strategy for making communication less of a constraint on the systems we can build.
What You'll Build
Characterise and simplify communication paths between accelerators, tracing latency and unnecessary overhead across networking, runtime, memory, and device layers
Develop faster data movement across heterogeneous hardware, exploring RDMA, programmable NICs, DPUs, switches, and software approaches to cross-device memory management
Build flexible mechanisms for transferring model state across accelerator types and execution strategies, including KV cache connectors across different forms of parallelism
Evaluate existing and emerging scale-up and scale-out fabrics, informing cluster architecture, infrastructure integration, and how heterogeneous accelerator communication should evolve
What Sets You Apart
Deep understanding of networking and communication systems, with the ability to reason across protocols, hardware, memory systems, and software layers
Experience with high-performance data movement such as RDMA, Ethernet fabrics, accelerator interconnects, programmable networking, or similar latency-sensitive systems
Strong systems performance instincts, with the ability to trace bottlenecks across abstraction layers and distinguish fundamental constraints from accidental ones
A demonstrable tendency to question existing abstractions, generalise across unfamiliar technologies, and simplify systems around the requirements of the workload
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.