London AI infrastructure startup Callosum raises $100M seed, sets European early-stage record
On August 20 Callosum closed a $100M seed round led by Atomico, with the UK's £500M Sovereign AI Fund making its first publicly disclosed investment.
On August 20, London-based AI infrastructure startup Callosum closed a $100M seed round led by Atomico with Plural and DCVC participating, plus the first publicly disclosed investment from the UK's £500M Sovereign AI Fund. Bloomberg reported the round as one of the largest seed rounds ever raised by a European startup.
Callosum was founded in 2025 by Cambridge neuroscientists Danyal Akarca and Jascha Achterberg. Its core product is systems software that decomposes AI workloads and routes each task to the cheapest model and chip that can handle it, rather than sending all tasks to top-end silicon. The round landed four days after Stripe agreed to acquire OpenRouter for about $7 billion, signaling that AI routing is being priced as infrastructure.
The UK Sovereign AI Fund was established by the UK government in 2026 with an initial £500M, aimed at providing sovereign-level capital for UK domestic AI infrastructure and foundation model R&D. Callosum is one of the fund's first publicly disclosed portfolio projects.