Callosum Raises $100M to Make AI Workloads Cheaper, With British State on Cap Table
Six months ago, the Cambridge startup Callosum left stealth with $10.25m. The valuation on the new round has not been disclosed. (August 20, 2026 - 8:50 am)
Credit: Callosum
Callosum has raised $100m, six months after its initial stealth exit, and the round includes investment from the British state. Bloomberg reported the raise, citing the UK’s public AI fund as a participant.
The Cambridge company emerged from stealth in February with $10.25m led by Plural, a 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, up to $100m or roughly £75m, were reported in May.
What Callosum offers is orchestration rather than silicon. Its software distributes an AI workload across mixed hardware—Nvidia, AMD, Google, and whatever else is available 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 this approach delivers twice the accuracy, seven times the speed, and a quarter of the cost of a conventional GPU setup for complex agentic work, such as autonomous computer use.
Founders Danyal Akarca and Jascha Achterberg met while pursuing their PhDs at Cambridge and have published in Nature journals, with prior stints at Intel and Google DeepMind. Their pitch challenges the prevailing architecture:
“Big labs are currently betting that one model will rule them all,” said one of the founders at launch. “We think that’s wrong.”
The state's involvement is noteworthy. 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, drawing parliamentary attention. Six other companies in the same announcement 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 vocal about this: Kendall’s line at the launch was that the government is “betting on Britain.”
Callosum enters an industry where the economics of inference have become a central problem rather than a footnote. While model training costs are concentrated in a handful of companies, the bill for running models falls on everyone—which has put pressure on Nvidia’s software moat this year from an unexpected direction.
It's also not the only British company offering a cheaper way to run AI. Velaura raised $110m for low-power inference chips, and UK AI startups are collectively valued at $256bn, according to a recent industry count.
The company’s framing draws on neuroscience; the corpus callosum is the bundle of fibres connecting the brain’s two hemispheres, and Callosum’s argument is that intelligence emerges from separate systems coordinating rather than from one very large one scaling further.