Callosum

Callosum became the first equity investment from the Sovereign AI Unit (SAIU) when DSIT named its inaugural cohort on 16 April 2026 . Callosum was founded by Cambridge PhD graduates Danyal Akarca and Jascha Achterberg to build chip-optimisation software enabling heterogeneous silicon fleets to interoperate.

The direct equity stake, unique among the seven first-cohort firms, marks Callosum out as the programme's highest-confidence bet: six other companies received compute access via the AI Research Resource, but only Callosum received a capital cheque. The SAIU's naming at Wayve's London HQ, one day after Wayve closed a large Series D extension, underscored that the Sovereign AI label is as much a hardware-alliance endorsement as a sector bet.

The chip-interoperability problem Callosum addresses is structural to European AI sovereignty. European data centres and research facilities increasingly run mixed fleets of Nvidia, AMD, Intel, and emerging European silicon. Without software that abstracts across architectures, workloads remain sticky to individual vendors, reproducing the lock-in that European sovereign cloud policy aims to eliminate. Callosum's equity backing positions it as an infrastructure layer below the model tier: if Cosine, Prima Mente, and the other SAIU investees are building British AI applications, Callosum is building the plumbing that lets those applications run on non-US silicon.