Callosum

Callosum sits between AI applications and the compute that runs them. As industry spending shifts from training models to running them, AI-native companies routinely spend half or more of their revenue on inference — largely because every workload is pushed through the same general-purpose hardware regardless of what the task actually requires. At the same time the chip market is fragmenting, with hyperscalers shipping custom silicon and a wave of specialised processors reaching production.

The company's software treats that fragmentation as an opportunity rather than a problem. Its platform decomposes a workload into its component tasks and assigns each one to the model and processor best suited to it, an approach it calls programmable heterogeneity. Its first product is a family of APIs that let developers adopt frontier AI hardware without rewriting their applications. The technical premise comes from the founders' neuroscience research: biological brains achieve general capability through varied specialised structures, not repetition of identical units.

Callosum was founded in 2024 by Cambridge PhDs Danyal Akarca and Jascha Achterberg and is based in London. It came out of stealth in February 2026 with a $10.25m round led by Plural, supported by ARIA and angels including Charlie Songhurst, Stan Boland and John Lazar. In August 2026 it raised a $100m seed led by Atomico with Plural, DCVC and the UK Sovereign AI Fund, becoming the first company backed by that fund. It has announced partnerships with chipmakers including Cerebras and Rebellions, and is named in the UK's £1.1bn AI hardware plan.