Nextop AI raises $500M at $4.2B for Ethernet networking built for AI clusters

The round closed March 10, 2026, and was led by Lightspeed, with a16z joining as a major investor. Altimeter and other existing backers also took part, and the company described the round as oversubscribed. The name is Nexthop AI, not Nextop. The valuation comes less than a year after the company left stealth with $110 million in March 2025. Three new switches built for AI data center traffic launched with the raise: the NH-4010, NH-4220 and NH-5010. They support 1.6 terabits per port, with dense configurations reaching 50-100+ terabits of aggregate throughput. Systems are co-designed with each hyperscaler's engineering team and run on open-source SONiC. One profile lists 300+ engineers, up from about 100 at launch. The timing tracks the capex wave. Alphabet, Amazon, Meta and Microsoft are expected to spend roughly $650 billion on AI data centers and related infrastructure in 2026. Network fabric is becoming a gating factor for cluster performance. For AI builders, networking is moving from an afterthought to a constraint on training and inference throughput. Custom, open-standard Ethernet from a well-funded vendor could widen supply options for neoclouds and large operators. Startups that rent GPU capacity may see the effect indirectly, through better cluster utilization and potentially more competition among providers.