London's Callosum banks $100M seed to rebuild AI infrastructure around heterogeneous chips

Callosum, a London-based startup building infrastructure for heterogeneous AI compute, has closed a $100 million seed round led by Atomico — one of the largest seed rounds ever raised in Europe.

The company's core thesis is that the dominant AI scaling approach — stacking identical chips and architectures — has reached its limits. Callosum argues that the problems AI is now being asked to solve are inherently heterogeneous, and that no infrastructure has existed to bring together the growing variety of chips and compute primitives arriving from different manufacturers and research labs. Its platform is designed to let heterogeneous silicon and AI models co-evolve within a single system, targeting what it describes as orders-of-magnitude improvements in both capability and cost.

Callosum positions itself not as a model builder but as an infrastructure layer operating at the systems level — spanning from silicon to production applications. The company says it publishes frontier research alongside engineering production systems, with the goal of serving both AI development teams working on complex problems and chipmakers whose hardware it integrates.

The $100 million raise will support continued development of that infrastructure stack and team expansion. Callosum is actively recruiting scientists, engineers, and what it calls high-agency builders across its technical disciplines.