Cosine Builds Britain’s Sovereign AI Coding Models on Isambard-AI

Cosine has positioned itself at the center of the UK's push for domestic machine learning infrastructure. Backed by the British government's £500 million Sovereign AI programme, the London startup was awarded 500,000 GPU hours on the Isambard-AI supercomputer at the University of Bristol to train Lumen Sovereign, an end-to-end frontier model that runs inside on-premises and air-gapped environments.

While mainstream AI developer tools rely on cloud APIs managed by American providers, Cosine focuses on organizations where transmitting proprietary source code outside secure perimeters is legally or operationally prohibited. As reported by Business Leader, the company has formed a coalition of roughly 35 UK organizations—including BAE Systems, Babcock International, HSBC, Lloyds Banking Group, NatWest, and BT Group—to define use cases, governance requirements, and domain datasets for sovereign enterprise models.

Air-Gapped Code Generation for Critical Infrastructure

Founded in 2022, Cosine builds foundation models and developer tools capable of operating in air-gapped facilities with zero connection to the public internet. Rather than fine-tuning off-the-shelf checkpoints, the team trains models from scratch using proprietary data pipelines designed to replicate developer reasoning steps.

In an interview with Resilience Media, co-founder and COO Yang Li explained that the platform's focus extends beyond typical modern web stacks to older programming environments: "In certain legacy coding languages, we’re twice as good as the frontier models, including COBOL, Fortran, Ada and, to a certain extent, even .NET." In defence applications, such support addresses specific operational bottlenecks, such as avionics software that only a dwindling number of senior engineers understand.

Alongside its flagship autonomous engineering agent, Genie, Cosine introduced its Lumen family of models in a video product launch. The family includes Lumen Outpost as its core model, Lumen Trail for on-premise workhorse tasks, Lumen Scout for retrieval and codebase mapping, and Lumen Frontier. The architecture emphasizes disciplined edits, avoiding dead code, and supporting codebases across more than 38 languages.

The Founding Team

Cosine was co-founded by Alistair Pullen, Yang Li, and Sam Stenner.

CEO Alistair Pullen, who studied computer science at the University of Exeter, has built software since childhood and previously saw an exit when delivery app Fancy was acquired by GoPuff. As reported by The Telegraph, Pullen and Li recognized the potential of large language models for software engineering after experimenting with GPT-3, later securing a place in Y Combinator’s W23 batch.

COO Yang Li previously served as Commercial Director at Mobike, scaling operations internationally to 220 million monthly active users prior to its acquisition by Meituan. He also held roles as Chief Growth Officer at Ziglu and Vice President of Europe for Digital Currency Group's consumer arm, Luno. Co-founder and CTO Sam Stenner, also a computer science graduate from the University of Exeter, heads technical development across the company's platform.

Sovereign Compute and On-Premises Economics

In addition to technical autonomy, Cosine pitches on-premises hardware as a more stable economic alternative to cloud token billing for high-throughput enterprise teams. As Li noted to Business Leader, purchasing dedicated GPU racks allows engineering organizations to run heavy interactive workloads by day and schedule background processing—such as static analysis and security scanning—overnight without incurring incremental per-token charges.

The venture arm of the UK Government’s Sovereign AI Fund holds the option to participate in Cosine’s next funding round. The startup has raised outside investment from institutional backers including Lakestar, SOMA Capital, Northern Powerhouse, and Gaingels.

Engineering and Platform Expansion

To build and harden systems for air-gapped customer environments, Cosine is expanding its engineering and technical outreach teams in London.

Infrastructure reliability underpins sovereign deployments. The company is hiring a Software Engineer, Cloud Infrastructure to construct core infrastructure, including Kubernetes environments, deployment pipelines, and networking stacks designed for large-scale enterprise deployments and isolated environments. The platform group is also adding a Senior Infrastructure Engineer (£75,000–£100,000) to own Kubernetes clusters, CI/CD pipelines, and observability tools, alongside a Senior Platform Engineer (£75,000–£100,000) tasked with building hardened configurations and platform services for regulated enterprise customers.

On the developer application layer, Cosine is recruiting a Product Engineer ($70,000–$90,000) to build end-user developer workflow tools that integrate Cosine's LLM technology, developing reactive applications and back-end APIs. To communicate its research to enterprise clients, the company is seeking a Senior Developer Evangelist (£60,000–£90,000) to scale technical storytelling across written, visual, and video formats and translate ML research for enterprise engineering leaders.

Open Positions at Cosine

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