Callosum
Site Reliability - Member of Technical Staff
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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.
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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
Our platform is the production system our customers route real traffic through. When it degrades, their product degrades. You will own its operational health end-to-end: SLOs, observability, incident response, deployment discipline, and capacity planning across heterogeneous compute backends. As the platform scales to millions of concurrent requests across heterogeneous compute, the work shifts from building the operational foundation to defending it under conditions most teams never encounter.
You'll define "production-grade" means for a platform at the centre of a fast-growing company, and own it end to end. The reliability practice is yours to build. You will work closely with the platform team, setting the technical direction. You will work closely with the hardware and orchestration teams to expose heterogeneous backends reliably through the platform.
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Who You'll Build
- Service-level objectives, monitoring, alerting, and observability
- On-call and incident response: runbooks, escalation, blameless postmortems, and follow-through
- Capacity planning and the operational side of running across heterogeneous compute backends
What You Bring
- Strong SRE or production-engineering background running customer-facing systems at scale
- Fluency with modern operational tooling: observability stacks, container orchestration, infrastructure-as-code, CI/CD
- Experience owning incident response and driving reliability improvements.
- Compliance execution experience
What Sets You Apart
- Open-source contributions to relevant infrastructure, or production systems whose scale and complexity you can speak to in detail
- Early-stage and AI-native company experience
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.
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