- Cosine, the UK government-backed AI startup, has assembled a coalition of major British institutions, including BT, Babcock International Group, Lloyds Banking Group, LSEG, NatWest Group, PwC, Thales UK, and Telefónica Tech UK&I, to co-design Lumen Sovereign, a frontier AI model to be trained entirely on British soil.
- The model will run on Isambard-AI, one of Europe’s most powerful supercomputers, using compute awarded through the UK government’s £500M Sovereign AI programme, with deployment readiness targeted for the end of 2026.
- For Cosine’s coalition partners, the proposition is simple: OpenAI and Anthropic are outstanding products, and for some of their most sensitive workflows, legally off the table.
Cosine has signed memoranda of understanding with some of the UK’s largest institutions to co-design Lumen Sovereign, a frontier AI model that will be trained entirely on UK infrastructure, deployed within customers’ own environments, and carry no dependence on foreign technology at any stage.
The coalition spans defence, finance, telecoms, and professional services. Babcock International Group, BT, Lloyds Banking Group, LSEG, NatWest Group, PwC, Thales UK, and Telefónica Tech UK&I have all signed on for the design phase.
The model will be trained on Isambard-AI, one of Europe’s most powerful supercomputers, using compute allocated through the UK government’s £500M Sovereign AI programme, which named Cosine among its first cohort of supported startups in April 2026. Deployment readiness is targeted for the end of 2026.
“AI is the single most important technology of our generation. Enterprises are increasingly waking up to the risk of being wholly dependent on foreign providers for this technology. Vendor lock-in creates security risk, dependency risk, and cost escalation risks,” says Alistair Pullen, CEO and co-founder of Cosine.
“Cosine is addressing those risks by building a model that is fully trained on UK soil and available into air-gapped environments — systems with no connection to external networks — at a far more efficient price point than OpenAI and Anthropic alternatives,” he adds.
The problem that cloud AI cannot solve
For most enterprise users, the choice of an AI model is a procurement question. For defence contractors, banks running know-your-customer investigations, and operators of critical national infrastructure, it is a legal and security question first.
Sending sensitive data to a server in a US data centre is not an option when the work involves classified systems, anti-money laundering alerts, or clinical data. The existing hyperscaler models were not built for this. Cosine’s argument is that retrofitting security onto a cloud product is not the same as building it from the start.
Founded in 2022 by Alistair Pullen, Yang Li, and Sam Stenner, a Y Combinator alumni team, Cosine has raised $8M from Lakestar, SOMA Capital, and Gaingels. The company’s models have outperformed OpenAI, Anthropic, Mistral, and DeepSeek on independent coding benchmarks for two consecutive years.
It already supports over 38 programming languages, including Fortran, COBOL, and Ada: the legacy languages that run Britain’s defence systems, nuclear infrastructure, and the backbone of financial services, and which most AI tools handle poorly.
Lumen Sovereign will be trained from scratch on proprietary datasets built entirely in-house, covering more than 30 regulated industry workflows, rather than being adapted from an existing open-source checkpoint.
What the coalition commits to
MOU signatories commit to working with Cosine to define the use cases, security requirements, and governance standards that the model must meet.
Priority applications reflect where UK AI adoption has stalled: cybersecurity and adversarial testing, KYC and AML alert investigation, clinical trial coordination, legal document review, and healthcare administration.
“As AI becomes a foundational technology for the UK economy, our customers need confidence that the systems they depend on are secure, trusted, and aligned with their requirements,” says Chris Keone, managing director of Innovation at BT.
Peter Passaro, director of AI and Data at Babcock International, was more direct: “Cosine has offered us a path to a completely UK native and highly customisable AI stack. Together, we can co-create and design AI models that are highly specific for the very complex defence environments we operate in.”
The credibility question
The UK has announced sovereign AI ambitions before. What makes this announcement different is the coalition.
BT, Babcock, Lloyds, and LSEG are doing it because they have a genuine problem, and Cosine is one of the few companies making a credible attempt to solve it on terms those institutions can accept.
Whether Lumen Sovereign will deliver by the end of 2026 remains an open question. Training a frontier model from scratch on bespoke datasets to meet the assurance standards required by defence and financial services is a formidable engineering and governance challenge.
What the UK government has understood, and what this coalition reflects, is that sovereign AI is not an ideological position. For the organisations that have signed on, it is a procurement requirement.
