Oxford photonics startup Salience Labs closes $125M Series B for optical GPU switching

Bullhound Capital led the oversubscribed round, and its principal Callum Stewart joins the board. AMD Ventures, Intel Capital, SBI Group, Hudson River Trading and British Business Bank (which confirmed a separate £10M contribution) also invested, alongside existing backers Applied Ventures, Oxford Science Enterprises, Cambridge Innovation Capital and Silicon Catalyst Ventures. No valuation was disclosed. Proceeds go to 128-port and 256-port optical circuit switches, volume manufacturing and a larger Silicon Valley presence. Salience was founded in 2021 on research from the universities of Oxford and Münster. Its switches route light between GPUs without converting it to electrical signals, which is meant to cut latency and power draw as clusters grow toward hundreds of thousands of accelerators. Optical circuit switching is a crowded race that also includes in-house efforts at large cloud operators. For AI builders, the network is turning into a bottleneck and a cost line in training clusters. Chipmaker venture arms on the cap table suggest where interconnect supply is heading, which matters for anyone planning multi-year capacity or negotiating cluster design.