AI Performance Modeller

Flux Computing designs and manufactures optical processors to train and run inference on large AI models. Join us to be part of a highly motivated and skilled team that thrives on delivering impact and innovation at speed.
The Role
We're searching for a Performance Modelling Engineer to create and own the analytical and simulation models that steer OTPU architecture and software evolution. You will build functional simulators as well as high-fidelity, cycle-accurate models of our optical compute system. This role is critical to explore "what-if" design spaces, and deliver insights that directly influence our software, hardware, and optical roadmaps. This role sits at the crossroads of hardware architecture, software tooling and machine-learning workload analysis, perfect for an engineer who loves data-driven decision-making and fast iteration.

Responsibilities

• Functional Simulator: Design, build, and maintain a functional simulator of the OPTU subsystem and full pipeline.
• Performance Simulator: Design and maintain architectural & cycle-accurate models of the OPTU subsystems and pipeline. Identify throughput, latency and utilisation hot-spots; propose architectural, or scheduling fixes.
• Workload Analysis & Bottleneck Hunting: Instrument benchmarks (LLMs, diffusion, graph workloads) to collect detailed traces.
• Design-Space Exploration: Run massive parameter sweeps with your functional and to understand tradeoffs and guide the software, hardware, and optical teams. Package results into clear, quantitative analyses and design recommendations.
• Tooling & Automation: Develop Python/C++ tooling for trace parsing, statistical analysis and visualisation. Integrate models into CI so that every RTL commit gets a performance smoke test.

Skills & Experience

• 3+ years building performance or power models for CPUs, GPUs, ASICs, or accelerators.
• Strong coding ability in C++ and Python; experience with discrete-event or cycle-accurate simulators (e.g., gem5, SystemC, custom in-house).
• Solid grasp of computer-architecture fundamentals: memory systems, interconnects, queuing theory, Amdahl/Gustafson analysis.
• Familiarity with machine-learning workloads and common frameworks (PyTorch, TensorFlow, JAX).
• Comfort reading RTL or schematics and discussing micro-architectural trade-offs with hardware designers.
• Excellent data-visualisation and communication skills: able to turn millions of simulation samples into one decisive slide.
• Bachelor's+ in EE, CS, Physics, Applied Maths or related; advanced degree preferred but not required.
• Personal or open-source projects in simulators, ML kernels, or performance analysis are a significant plus.

Compensation & Benefits

• £126,000 – £154,000 annual salary, depending on experience, skills, and location.
• Competitive stock options, you're not just part of the journey, you will own a piece of it.
• Work from our HQ in King's Cross, right in the middle of London's buzzing AI scene.
• Live within 45 minutes of the office? Perfect. Live within 20 minutes? We'll add an extra location bonus to your salary.
• We offer visa sponsorship and full relocation support (UK and abroad), through a dedicated third-party provider who are on hand to make your move to London as seamless as possible.
• Full BUPA healthcare and dental cover, medical history disregarded.
• High-spec tech for everyone - M4 Macs as standard, M4 Pros for Engineers.
• Sony noise-cancelling headphones and ergonomic setups to keep you comfortable and focused.
• Personal company card to spend on tools that help you do your job - like ChatGPT Pro or anything else that boosts your workflow.
• Healthy, chef-cooked dinners in the office every night, with something for every diet and tastebud.
• Monthly off-site team socials.
• 25 days of paid holiday, plus all the UK bank holidays.
• Access to our in-house 3D printer for personal or work projects.
• Cycle2work scheme.
• Need a caffeine fix? We've got you covered with a tab at our favourite local coffee shop.
• We offer a pension plan and salary sacrifice options.

We do not accept unsolicited CVs from recruitment agencies, will not be liable for any fees, and prohibit unauthorised use of our company name in recruitment activities.
We're building fast and that includes our benefits. More exciting additions are coming soon for the Flux crew.
If you are passionate about pushing the boundaries of what's possible in AI and thrive in a high-energy, fast-paced environment, we want to hear from you. Apply now to join Flux and be a key player in shaping the future of computing.