Callosum raises $100M seed led by Atomico to break the AI compute monoculture
August 20, 2026
Callosum, the London AI infrastructure company co-founded by Danyal Akarca, has raised a $100m (£73.8m) seed round led by Atomico, with participation from Plural, DCVC and the UK's £500m Sovereign AI Fund.
The round lands against a shift in where AI money goes. Spending is moving from training models to running them, and AI-native companies now routinely hand over half or more of their revenue to inference costs. Most of that compute passes through the same general-purpose hardware whatever the task demands of it. Meanwhile the silicon market is pulling apart in the opposite direction — hyperscalers are shipping their own custom chips and a wave of specialised processors, from wafer-scale to optical, is reaching production. There has been no serious software layer for making use of that variety.
Callosum's platform decomposes a workload into its component tasks and assigns each one to the model and processor best suited to it, an approach the company calls programmable heterogeneity. Its first product, live from launch, is a family of APIs that let developers reach frontier AI hardware without rewriting their applications. The premise comes from the founders' research background: brains get general capability out of varied specialised structures rather than repetition of one unit, and Callosum argues intelligence built on silicon should work the same way. Alongside the raise the company announced partnerships with US chipmaker Cerebras and South Korean semiconductor startup Rebellions.
Akarca founded the company in 2024 with Jascha Achterberg, whom he met while both were completing PhDs at Cambridge across neuroscience, computing and AI. Callosum came out of stealth in February 2026 with a $10.25m round led by Plural, backed by ARIA and angels including Charlie Songhurst, Stan Boland and John Lazar. On complex agentic tasks such as autonomous computer use, the company has claimed roughly twice the accuracy, seven times the speed and a quarter of the cost of single-architecture setups, though it has not published the benchmark methodology behind those figures.
The raise is among the largest seeds a European AI infrastructure company has announced, and Callosum is the first business to take money from the UK's Sovereign AI Fund. It has also been named in the government's £1.1bn AI hardware plan. "AI is nothing without the chips that underpin it, and the eye-watering demand for them is only going to grow," UK AI minister Kanishka Narayan said in a statement, adding that success will turn on using those chips efficiently rather than merely securing access to them. The money is earmarked for scaling the platform and expanding the London team.
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