The racks will run through a partnership with Callosum, a London-based AI compute startup that last week raised about $100 million in seed funding led by Atomico, with backing from the UK's Sovereign AI Fund.
"The partnership with Callosum allows our chips to work alongside other specialized hardware, with different components handling different parts of an AI workload," said Rebellions Chief Executive Park Sung-hyun.
Callosum was the fund's first disclosed equity investment.
Founded in 2025 by two Cambridge University neuroscientists, Callosum develops software that routes AI workloads to the chips and models best suited to each task.
Rebellions will join as Callosum's lead partner in Asia. The two companies are jointly designing a reference architecture that positions Rebellions' NPUs as inference-only hardware within Callosum's heterogeneous computing platform, allowing customers to deploy NPU-based infrastructure without separate optimization work.
Rebellions said the initial supply of more than 100 racks would mark the first phase of the project, with further shipments expected in later stages as it seeks to accelerate its push into sovereign AI markets across Britain and Europe.
The European breakthrough comes at a pivotal time for Rebellions, one of South Korea's most closely watched unlisted semiconductor companies.
Founded in 2020 and based in Bundang, south of Seoul, Rebellions develops data-center AI accelerators designed primarily for inference, the process of running trained AI models to generate answers and other outputs.
The company has raised roughly $850 million from investors including SK hynix, Samsung Ventures and Arm, as well as the South Korean government, and was most recently valued at around $2.3 billion.
Rebellions has been preparing for an eventual stock-market listing rather than publicly pursuing a sale. Chief Financial Officer Shin Sung-kyue said last year that an initial public offering remained the company's "master plan."
The company raised more than $400 million in a pre-IPO financing round in March, when it also introduced two rack-scale AI infrastructure products, RebelRack and RebelPod.
It confirmed its CEO Park has met with Nvidia Chief Executive Jensen Huang at Nvidia's Santa Clara headquarters last week without disclosing the details.
AJP Takeaways
• The racks run through Callosum, a London startup that raised about $100 million led by Atomico and was the first disclosed investment of the UK's Sovereign AI Fund.
• Rebellions' ATOM NPUs pair with Callosum's vendor-neutral routing layer, positioning the Korean chipmaker against Nvidia's dominance in inference hardware.
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