London startup Callosum raises €85.4 million led by Atomico to unify AI models and chips

London-based startup Callosum has closed an €85.4 million ($100 million) Seed funding round led by venture capital firm Atomico. The round also saw participation from Plural, DCVC, and the UK Sovereign AI Fund, along with other investors.

The company develops software designed to efficiently combine different AI models with different types of computer chips, an approach it calls "heterogeneous intelligence." Atomico CEO Niklas Zennström said that as AI shifts from training toward practical deployment, success depends not only on building the best models but also on efficiently directing AI workloads to the right computing resources.

The new round follows an €8.76 million pre-Seed raise announced in February, led by Plural. Callosum was founded in 2025 by Jascha Achterberg and Danyal Akarca, based on the idea that the future of AI hinges not on owning the biggest model or infrastructure, but on the ability to coordinate many different models across diverse types of hardware.

Callosum is also the first-ever investment made by the UK Sovereign AI Fund, and the company has been named in the UK government's £1.1 billion AI hardware plan. UK Minister for Artificial Intelligence Kanishka Narayan stressed that success in AI will depend not only on access to chips but on using them as efficiently as possible.

New partnerships and product rollout

Alongside the funding news, Callosum announced several global compute partnerships, including one with Cerebras Systems and another with chipmaker Rebellions. The company also introduced what it calls "programmable heterogeneity" — the ability to break AI tasks into smaller components and route each to the model and chip best suited to it based on cost, energy, and speed requirements.

The third announcement concerns the production rollout of its "Tailored Inference" product, a family of APIs already showing performance and cost improvements in fields such as cybersecurity and finance. Callosum's team includes specialists from Cambridge, Oxford, MIT, Imperial College London, Microsoft, ETH Zurich, and Intel, with operations spanning the UK and US.