Callosum Raises $100M to Make AI Workloads Cheaper with UK Sovereign AI Fund Backing

Callosum raises $100m to make AI workloads cheaper, with the British state on the cap table

Six months ago the Cambridge startup left stealth with $10.25m. The valuation on the new round has not been disclosed Callosum has raised $100m, six months after leaving stealth with a tenth of that, and the round includes money from the British state. Bloomberg reported the raise, describing the UK's public AI fund as a backer. The Cambridge company came out of stealth in February with $10.25m led by Plural, the fund founded by former Wise executive Taavet Hinrikus, alongside the government research agency ARIA and angels including Charlie Songhurst, Stan Boland, and John Lazar. Talks about a much larger round were reported in May, at up to $100m, or roughly £75m. What Callosum sells is orchestration rather than silicon. Its software distributes an AI workload across mixed hardware, Nvidia, AMD, Google, and whatever else is in the rack, routing each part of a task to the chip and model that handle it best instead of assuming a homogeneous grid of GPUs. The company claims that on complex agentic work, such as autonomous computer use, this delivers twice the accuracy, seven times the speed, and a quarter of the cost of a conventional GPU setup. The founders are Danyal Akarca and Jascha Achterberg, who met while doing PhDs at Cambridge and have published in Nature journals, with stints at Intel and Google DeepMind between them. Their pitch is a direct bet against the prevailing architecture: "Big labs are currently betting that one model will rule them all," one of them said at launch. "We think that's wrong." The state's involvement is the part worth reading twice. In April, Callosum became the first equity investment made by the UK's Sovereign AI Unit, a £500m vehicle chaired by James Wise and launched with backing from technology secretary Liz Kendall and chancellor Rachel Reeves. Neither the cheque size nor the equity stake was disclosed at the time, and it has not been disclosed since, a gap that has already drawn parliamentary attention. Six other companies in the same announcement, among them Cosine, Prima Mente, Cursive, Doubleword, Twig Bio, and Odyssey, received up to a million GPU hours each on national supercomputing capacity rather than cash. "The UK enjoyed a depth of talent across universities and labs like DeepMind," Akarca said of the decision to build in Britain, calling it the natural place for the company. Ministers have been unusually keen to say the same thing in public: Kendall's line at the launch was that the government is "betting on Britain". Callosum is arriving at a moment when the economics of inference have become the industry's central problem rather than a footnote. Model training costs are concentrated in a handful of companies, but the bill for running models sits with everyone, which is why Nvidia's software moat has come under pressure from an unusual direction this year. It is also not the only British company selling a cheaper way to run AI. Velaura raised $110m for low-power inference chips, and UK AI startups collectively are now valued at $256bn, according to a recent industry count. The company's framing borrows from neuroscience, which is not a marketing flourish in this case. The corpus callosum is the bundle of fibres connecting the brain's two hemispheres, and the founders' argument is that intelligence emerges from separate systems coordinating rather than from one very large one scaling further. Whether that holds as an engineering thesis is still an open question in the field. It is, however, a considerably easier thesis to fund in Britain than a plan to build a frontier model, given the capital gap between UK investors and the American labs. Several things about the round remain unpublished. Bloomberg's report did not disclose a valuation; the full investor list has not been confirmed by the company, and it is not clear how much of the $100m came from the Sovereign AI Unit as against private funds. Companies House filings should settle the ownership question in the next quarter, which is a slower answer than a press release but a more reliable one. Callosum had not published a statement of its own at the time of writing.

UK AI start-up Callosum secures $100m in seed funding round

The company aims to lower AI costs by attaching each task to the model and hardware that best suits it. Callosum, a UK-founded AI start-up that develops software to match specific AI tasks with the least expensive and most suitable models and chips, has raised $100m in early seed feeding. The round was backed significantly by the UK's Sovereign AI Fund and led by venture capital firm Atomico with additional participation from investors Plural and DCVC. The organisation also has a partnership with chipmaker Cerebras Systems and has deals with Rebellions Inc and Axelera AI. Established in 2025, by two Cambridge University neuroscientists, Danyal Akarca who is the CEO and CTO Jascha Achterberg, Callosum software can direct specific AI tasks towards the models and chips best suited to the activity and financial requirements, as a means of showing that not every company requires high-end, powerful graphic processors or AI strategies. Callosum was the first investment to be disclosed by the UK's Sovereign AI fund, which launched in April of this year. Kanishka Narayan, the UK minister for AI, said, "AI is nothing without the chips that underpin it and the eye-watering demand for them is only going to grow. In the race to develop and use AI, success will depend not just on having access to those chips, but on using them as efficiently as possible." In the race to develop the most efficient, cost-effective and powerful chips, a range of organisations globally have invested significant time, money and effort into expanding their capabilities. This week, UK AI hardware start-up Fractile announced it is in talks to raise funding of roughly $600m at a pre-money valuation of $6.5bn. Fractile aims to enable the scaling of cheaper AI token processing for faster model reasoning. US AI company Etched raised $700m in a new funding round led by US trading firm Jane Street. The organisation builds inference clusters to make AI inference faster, cheaper and more efficient. In March of this year, global leader in the AI and chips space Nvidia, announced a new multi-year partnership with Thinking Machines Lab, which will be using Nvidia's systems to train its AI frontier models. Don't miss out on the knowledge you need to succeed. Sign up for the Daily Brief, Silicon Republic's digest of need-to-know sci-tech news.