Intelligent Systems Engineer

About Us

Artificial intelligence scaled on a bet - that bigger models, more identical chips, and more data would keep delivering. As problems grow more complex and the requirements of intelligence more diverse, that bet is breaking down. The next era belongs to heterogeneous intelligence: diverse models on diverse chips, each with distinct strengths, co-evolving into systems of capability unreachable by any single model or accelerator. Callosum is the Intelligent Systems company. We built the infrastructure to make that possible. Our co-evolution engine optimises simultaneously across workflows, agents, and silicon. We launched in early 2026 showing orders of magnitude improvements in performance and a shift in the cost-performance frontier that no single chip or model provider can provide. We believe intelligence comes from the system, not the model. We are scientists and engineers solving what others consider impossible. If you thrive on hard problems, and are passionate and energised by the scale of the challenge, we'd love to hear from you.

About the Role

Intelligence comes from the system, not from any single model. Designing those architectures is the core of Callosum's work - and the core of this role. You will design new intelligent systems: configurations of models, decomposition strategies, and coordination patterns that outperform frontier monolithic equivalents on the workloads our customers actually run. The work spans the full arc - from translating an ambiguous customer problem into a precise architectural hypothesis, to prototyping and benchmarking against frontier baselines, to handing a validated design to the team that ships it into production. You will work closely with our forward-deployed engineers, who surface the hardest customer problems, and with engineers on the silicon side of co-design, who expose new hardware properties you can exploit. The systems you build enter our catalogue and get served at scale. This role sits on the software side of co-design. There is a hardware counterpart focused on silicon-level work; the two collaborate continuously.

Who we are looking for

• Substantial hands‑on experience with modern LLMs - not at the API‑consumer level, but at the level of someone who has trained, fine‑tuned, served, or built non‑trivial systems on top of them and understands what is happening underneath.
• Strong production engineering: you ship code, not notebooks.
• Empirical rigour: you benchmark honestly, profile before optimising, and do not claim wins you have not measured.
• The ability to operate without supervision on problems whose shape is not yet clear.

What Stands Out

• Direct experience with multi‑agent or compound systems, LLM inference and serving, reinforcement learning, distillation and fine‑tuning, programmatic prompt or topology optimisation, or structured and constrained generation.
• Open‑source work, research publications, or production deployments at meaningful scale.
• A history of sitting close to users or domain experts and translating their problems into systems that solve them.

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.