Australian AI cloud firm Firmus is investing in a subsea cable project being developed by SubCo.

The companies this week announced that Firmus would become a cornerstone customer on SubCo's upcoming APX East submarine cable system.

Firmus will invest US$300 million to secure up to 150Tbps of dedicated capacity over 25 years on the cable.

Bevan Slattery, founder and co-CEO of SubCo, said: "The connectivity requirements of AI are fundamentally reshaping demand patterns on international subsea routes. Firmus' decision to anchor capacity on APX East validates what we've been working toward – building the secure hyper-connectivity needed across the Indo-Pacific region for the next generation."

Plans for APX East were first announced in January. The 16-fiber-pair system is set to connect Australia to the US, running from the north of Sydney in New South Wales to San Diego, California. The cable’s landing station in Australia will be at NextDC’s S1/S2 site in Sydney.

APX East is expected to be Ready for Service in Q4 2028. A Hawaii branch is to follow in Q4 2029, and a Fiji branch is also planned.

Tim Rosenfield, co-CEO and co-founder of Firmus, added: "This is a 25-year investment in Australia's future. AI is fast becoming one of Australia's next major export industries, but that opportunity will only be realized if we invest in the infrastructure that underpins it.”

He continued: "At Firmus, we're building a network of AI Factories across Australia. But building the compute is only part of the challenge. We also need to reliably connect that infrastructure to the world.

"Securing up to 150 terabits per second of dedicated capacity gives us the scale and performance to connect Australian AI infrastructure directly with the United States, ensuring the AI infrastructure we build here can reliably serve the world's leading AI-Natives."

Founded in 2019, Firmus was initially focused on crypto and high-performance compute, specializing in immersion cooling, but today describes itself as a pure ‘AI factory’ builder. Its Project Southgate is a long-term initiative to design and deploy sovereign compute in Australia for AI training and inference, according to the company, with plans to deploy 1.6GW of capacity through to 2028. The company uses its HyperCube, a proprietary electrical and cooling system, claiming the system uses liquid cooling to remove heat more efficiently than traditional air-based systems.

The Nvidia-backed company has a small existing facility in Tasmania but is developing a 90MW data center in Launceston, a 52MW site in Wesley Vale, and a 288MW project in Bell Bay. Firmus is also partnering with CDC to roll out capacity on the mainland and targeting some 1.6GW of infrastructure by 2028.

This will be the second project Firmus and Subco have partnered on. In June, the pair announced plans for a subsea cable connecting mainland Australia to the island of Tasmania.

SubCo has previously said the APX East system will be the first between Australia and the United States not requiring optical regeneration, instead capable of being single-end powered, fed across the entire system. It will be the longest such system in the world. Subsea cables traditionally require repeaters every 100km (62.1 miles) or so to boost the signal.

SubCo, part of Slattery’s Soda Group, also owns the Oman Australia Cable and has capacity on the Indigo subsea cables. The company is developing the SMAP cable linking Sydney, Melbourne, Adelaide, and Perth.

Firmus also has an immersion-cooled GPU deployment in an STT GDC facility in Singapore through its SMC cloud unit. The company is also deploying GPU capacity in Batam, Indonesia.