Britain’s grand sovereign AI plan is managing to look a bit pants, with the entire scheme depending on Cosine, a London start-up with about 30 staff and $15 million raised.
According to the Financial Times, Cosine, founded by chief executive Alistair Pullen and Yang Li, is building Lumen Sovereign, a frontier AI model with government backing.
The project is being developed with companies including BAE Systems, PwC and Lloyds Banking Group.
Officials have called it “Britain’s first fully sovereign frontier AI model”, but critics are less dazzled and wonder whether Cosine has the talent, computing power and cash to pull off such a large job.
“We do have a track record in this field. We have done real large-scale work on large models and genuinely improved their performance,” Pullen told the FT.
Governments are getting twitchier about AI sovereignty and control of critical technology, especially when overseas labs can change access rules overnight.
Days after the UK said in June 2026 that Cosine would get access to its Isambard supercomputer, the US temporarily barred foreign groups from Anthropic’s Mythos and Fable models.
That sharpened worries about national security and dependence on foreign AI providers, which is the sort of thing ministers notice after the stable door has bolted.
The obstacles remain ugly. Cosine has raised just $15 million, while France’s Mistral has attracted billions and OpenAI and Anthropic have swallowed far larger sums.
Cosine is one of a small number of UK companies trying to build frontier AI models from scratch. That field is dominated by flush US and Chinese groups that can throw compute at problems until the lights flicker.
Pullen said Cosine was not trying to match OpenAI and Anthropic across every use case. Instead, the company has trained and adapted large language models for customers in regulated industries, including financial services and defence.
Those customers need AI systems that can run on their own servers, which is less glamorous than chatbots but rather useful when compliance bods are breathing down your neck.
Pullen argues that this work gave Cosine the base needed for Lumen Sovereign.
“The kind of work that you need to do to build the model from scratch is very similar to all the work we’ve done in the past, at maybe a couple of orders of magnitude increased size,” he said.
Cosine was founded in 2022 after Pullen decided large language models would transform software development.
He and Li, previously an executive at technology start-ups including collapsed payments group Ziglu and cryptocurrency exchange Luno, set out to build an “AI software engineer”.
After joining Y Combinator, the pair gained early access to OpenAI’s models and fine-tuned them for software engineering tasks. Bigger rivals quickly built a lead in autonomous coding tools, especially Anthropic with Claude Code.
That forced a rethink. Rather than take on the biggest AI labs directly, Cosine shifted towards AI systems for regulated industries.
That move now gives the company a more credible story for Lumen Sovereign than another doomed coding assistant with a hoodie and a pitch deck. Cosine is building the model using a “mixture of experts” framework, an approach popularised by China’s DeepSeek.
Its architecture is based on Mistral’s Large 3 model, although Pullen said Lumen Sovereign would be roughly twice the size.
The biggest limit is compute. Pullen estimates Isambard will provide about 80 per cent of the training capacity needed. The remaining compute will come from private UK data centres, assuming the machinery, energy and patience are all available at the same time.
Unlike OpenAI and Anthropic, Cosine does not plan to operate the model itself. It wants others to deploy Lumen Sovereign, dodging the colossal cost of running AI models at scale.
One venture capitalist familiar with Cosine said: “The tech seems great… they need to raise hundreds of millions of pounds of investment to be remotely competitive, and at the moment they are quite early in that journey.”
For scale, £100 million is about €117 million at recent exchange rates, so “hundreds of millions” is still a serious mountain for a 30-person outfit.
Pullen admits the challenge. Cosine hopes to share “checkpoints”, or snapshots of Lumen Sovereign during training, with partners by September 2026.
A wider public release is planned for October 2026, with a fundraising round due later in the year to pay for the next stage. The cash would fund an aggressive hiring push.
Cosine has yet to hire researchers from the world’s leading AI labs, and Pullen concedes it cannot match OpenAI or Anthropic pay packets.
Instead, he hopes the chance to build a frontier model in a small team will attract engineers who have become “pigeonholed” inside bigger outfits.
Sceptics think the lack of funding available to UK start-ups will clip Cosine’s ambitions before they get airborne.
Pullen said: “Look, we can show that we can do it. We can definitely pull this off.”
