September 17, 2026
When Rubin clusters went live, Lumentum and Coherent outran the cloud provider making the announcement.
Chip stocks have spent the past three months absorbing some of the worst sentiment in years. Nasdaq 100 futures slid around 1% last week as a coalition of AI executives endorsed slowing AI development, and chip stocks are down roughly 20% from June, qualifying as a bear market. The working assumption across much of the market has been that the AI infrastructure build is pausing, or at least wobbling.
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Wednesday offered a different data point.
CoreWeave on September 16 announced the bring-up of multi-rack NVIDIA Vera Rubin NVL72 on CoreWeave Cloud, putting hundreds of NVIDIA Rubin GPUs into a single scale-out cluster for agentic AI. Chen Goldberg, executive vice president of product and engineering at CoreWeave, said CoreWeave was the first AI cloud provider to validate and bring up a Vera Rubin NVL72, and to demonstrate that the rack-scale architecture could operate as a reliable, high-performance cloud service. That is not a roadmap slide. It is production.
A single NVIDIA Vera Rubin NVL72 rack pairs 72 Rubin GPUs with 36 Vera CPUs, NVIDIA NVLink 6, ConnectX-9 SuperNICs and BlueField-4 DPUs. CoreWeave’s multi-rack approach uses NVIDIA Spectrum-6 Ethernet switches to unify racks of accelerators into one coherent cluster. Connecting hundreds of those GPUs across racks in a live cloud environment is an engineering milestone that shifts the Rubin generation from paper launch to billable capacity.
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The company also introduced two new capabilities in CoreWeave AI Object Storage: cross-region write acceleration and a new Archive tier. The storage updates are intended to keep data closer to GPUs and reduce delays for AI workloads that depend on repeated model calls, tool use and access to intermediate data. For agentic workloads, where a model may call external tools dozens of times per task, latency at the storage layer compounds quickly.
CRWV rose roughly 4% on the news, snapping a five-session losing streak. But the more instructive moves came from the suppliers.
Lumentum stock rallied on Wednesday as optical networking shares rebounded from a sharp AI-related selloff earlier in the week. The stock gained about 8% to around $907, making Lumentum one of the best-performing stocks in the S&P 500 during the session. Coherent shares rose about 6% to roughly $287 in morning trading. Both names outpaced the cloud provider whose announcement was the headline catalyst.
The reason is supply math. Pump laser shipments rose more than 80% year over year and remain effectively sold out. Lumentum still expects a fourfold shipment increase over the next several quarters. Every multi-rack Rubin cluster CoreWeave brings online needs optical interconnects, transceivers, and pump lasers to move data between racks at the speeds those GPUs demand. Lumentum remains significantly behind customer demand for high-powered lasers, with the demand signal increasing faster than the ability to supply.
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Lumentum’s fiscal Q4 2026 revenue of $1.006 billion more than doubled year-over-year, up 109.3% from $480.7 million. Non-GAAP gross margin expanded sharply to 50.4%, up 1,260 basis points from a year ago, reflecting the operating leverage now embedded in the business. That is not a company riding a single quarter of enthusiasm. It is a company structurally undersupplied against a demand curve that just got steeper.
The risks are real. Coherent jumped about 6% and Lumentum climbed in a session where SOXX gained about 2% and SPY about 0.3%, making the optics group’s surge a positioning-only bounce confined to the sector. Some of Wednesday’s move was short covering after weeks of selling, not purely a fundamental re-rating. Valuation multiples for both names remain well above their historical averages. And AI customers could cut large-scale training spend faster than CoreWeave can monetize new capacity, which would eventually soften the demand signal flowing to optical suppliers.
The broader picture, though, is that CoreWeave has said nine of the ten leading foundation model providers rely on its platform, and the first Rubin-generation multi-rack cluster to go live commercially does so on that system. Every incremental cluster of that scale requires more fiber, more lasers, more transceivers. The companies most undersupplied against that pull may be worth watching more carefully than the cloud provider getting all the headlines.
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