Compensation reflecting your experience and skills.

About Us

Artificial intelligence scaled on a bet - that bigger models, more identical chips, and more data would keep delivering. As problems become more complex and the requirements of intelligence more diverse, that bet is breaking down.

We believe that the next era of AI belongs to heterogeneous intelligence: diverse models on diverse chips, each with distinct strengths, working together into something greater than the sum of their parts. Novel accelerators are emerging from every direction, but no infrastructure exists to bring them together. We are building it.

Callosum is the Intelligent Systems company. We believe intelligence comes from the system, not the model - where chips and models co-evolve to unlock discoveries unreachable under the current paradigm.

We are scientists and engineers solving what others consider impossible. If you thrive on hard problems, are passionate and energised by the scale of the challenge, we'd love to hear from you.

About the Role

As the Simulation Systems Engineer, you will be responsible for building heterogeneous hardware simulation tools, interpretable and actionable. You will work on the high-performance simulation engine for novel accelerators, interconnect technologies and experimental hardware.

Simulation sits vertically across everything Callosum builds, letting us deliver outcomes our partners can't get anywhere else.

This role has growth potential towards technical leadership in simulation architecture, performance modelling, and strategy.

Responsibilities

• Own development of Callosum’s simulation engine, from core design to API extensibility.

• Build and maintain high-fidelity models of heterogeneous compute environments, including latency, throughput, memory bandwidth, and cost.

• Drive performance: profile, benchmark, and continuously improve the simulation engine across latency, throughput, and resource efficiency.

Skills & Qualifications

• Master’s or equivalent practical experience in a relevant technical field

• Strong expertise in C++17/20 and low-level performance tuning

• Experience optimising performance-critical paths: memory layout, concurrency, asynchronous systems, cache efficiency

• Familiarity with simulation-oriented architecture patterns: event-driven systems, scheduling models, loose coupling, API extensibility

• Proficiency in CMake, Docker, and build management

Nice to have

• Experience with discrete-event simulation frameworks or HPC workload modelling

• Familiarity with distributed systems concepts

• Exposure to cloud infrastructure or novel compute environments

• Experience building Python bindings or interoperability layers for C++ systems

What we offer

• Competitive Salary: £101,000 - £192,000, determined by skills and experience.

• Equity & Ownership

• Medical and dental 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.

Compensation Range: £101K - £192K