London-based Callosum has closed a $100m (£73.5m) seed round led by Atomico, with Plural, DCVC and the UK Sovereign AI Fund participating. It is the first investment made by the government's £500m sovereign fund and one of the largest seed rounds ever raised by a British company.
Callosum was founded in 2025 by Cambridge neuroscientists Jascha Achterberg and Danyal Akarca. The company builds systems software that breaks an AI workload into smaller tasks and routes each one to whichever model and chip can handle it most cheaply and quickly — an approach it calls "heterogeneous intelligence".
The thesis runs against the prevailing view that greater capability comes from scaling a single frontier model across identical silicon, a strategy that concentrates spending on a narrow group of chip and model vendors.
The round was led by Atomico, with what the company describes as significant participation from Plural, DCVC and the UK Sovereign AI Fund, alongside angel investors. A valuation was not disclosed.
The cheque is the first deployed by the Sovereign AI Fund, the £500m vehicle launched by the government in April 2026 to back British AI companies in areas judged strategically important to growth and national security. Callosum has also been named in the government's £1.1bn AI hardware plan.
The step-up is steep. Callosum emerged from stealth in February 2026 with a $10.25m pre-seed led by Plural, which drew 22 investors and support from the Advanced Research + Invention Agency. Six months later it has raised roughly ten times that figure at the same nominal stage, leaving a cap table that now pairs conventional venture money with a state-backed investor.
"As AI moves from training to inference, the question is no longer just who builds the best models. It's how we deliver intelligence efficiently, across an increasingly diverse landscape of models and chips," said Niklas Zennström, chief executive of Atomico. He described Callosum as building "the software layer that intelligently routes AI workloads to the right compute".
Alongside the raise, Callosum disclosed a set of compute partnerships. The flagship agreement is with Cerebras Systems, aimed at delivering low-latency, multi-agent workloads at scale, with further tie-ups covering chipmaker Rebellions and other infrastructure providers and original equipment manufacturers.
"By integrating Cerebras into Callosum's platform, we're making ultra-low-latency inference available exactly where it creates the greatest impact," said Andrew Feldman, chief executive of Cerebras.
Kanishka Narayan, the minister for artificial intelligence, framed the investment in efficiency terms. "AI is nothing without the chips that underpin it — and the eye-watering demand for them is only going to grow," he said. "Success will depend not just on having access to those chips, but on using them as efficiently as possible."
The proceeds will fund engineering hires and the expansion of Callosum's partner network.
Original source: UKTN
