Big Tech's most important infrastructure is at the bottom of the sea (sherwood.news)

Amazon announced Fastnet, a new transatlantic subsea fiber linking Maryland to County Cork, Ireland with over 320 terabits per second of capacity (roughly 5,500 km of cable). The announcement underscores that submarine fiber — not on‑land data centers or satellites — carries about 99% of international network traffic. Amazon says Fastnet can transmit “the entire digitized Library of Congress three times every second,” illustrating the raw throughput these cables deliver and why they’re foundational to global cloud services and high‑bandwidth AI workflows. Big Tech is racing to own capacity and routing diversity: Amazon has roughly 30,000 km of subsea projects (and claims >9 million km when counting terrestrial fiber), Microsoft co-owns the 6,600 km MAREA transatlantic “open cable,” and Meta plans Project Waterworth (50,000 km) with deep‑water routing and enhanced burial to reduce damage risk; Meta also helped build the 45,000 km 2Africa Pearls system. Google leads with access to ~267,000 km across 33 projects and has built private cables like Dunant, Curie, Grace Hopper and Equiano. Technical implications for AI/ML include massive intercontinental bandwidth for distributed training and model serving, lower latency and greater control via private routes, but also concentrated physical vulnerabilities (cable cuts, geopolitical chokepoints) that make redundancy, routing diversity and upgradeable/open systems critical design considerations.