Plural participates in Callosum's $100M seed funding round
Callosum, a London-based AI infrastructure company, has raised $100 million in seed funding, one of the largest seed rounds ever raised in Europe. The round was led by Atomico, with significant participation from EstVCA member Plural, alongside DCVC, the UK Sovereign AI Fund, AlbionVC and other investors. Plural describes the investment as doubling down, having led Callosum's $10.25 million pre-seed in February 2026 when the company came out of stealth.
Formed in 2025, Callosum was founded by Danyal Akarca, its CEO, and Jascha Achterberg, its CTO, who met while completing PhDs in computational neuroscience at Cambridge. Their research examined how the brain produces intelligence by combining specialised circuits rather than repeating one type of neuron.
Most AI workloads run on the same general-purpose hardware regardless of what the task actually needs, which becomes expensive as industry spending shifts from training models to running them. At the same time the chip market is fragmenting, with specialised processors reaching production alongside established GPUs. Callosum's software breaks a workload into its component tasks and sends each one to the model and chip best suited to it, weighing cost, speed and energy. Its first product, a family of APIs called Tailored Inference, launched alongside the round and lets developers adopt new hardware without rewriting their applications.
The platform is already in production. On complex agentic workloads in financial services, Callosum reports it ran four times faster, cut compute costs by 70% and improved task success rates by 10% against the same work on a single frontier model and conventional GPU infrastructure.
Ian Hogarth, Partner of Plural, said results like these are the real case for heterogeneous compute: "frontier performance doesn't have to run through one dominant chip supplier or on one dominant model." That, he argued, will in turn determine who controls the infrastructure the rest of the economy runs on.
Alongside the round, Callosum announced a flagship partnership with Cerebras and further silicon partnerships across South Korea, the Netherlands and the UK. It is the first investment of the UK Sovereign AI Fund, the £500 million vehicle launched in April 2026, and has been named in the UK's £1.1 billion AI hardware plan. The funding will go towards scaling the technology, deepening silicon partnerships and expanding the team.
As AI spending shifts from training to inference, the question of which model runs on which chip is becoming an economic one rather than a purely technical one, and the software layer that answers it is drawing serious capital.
For more information, please visit Callosum's announcement.
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