NVIDIA Quantum-X800
Quantum-X800 is NVIDIA's XDR-generation InfiniBand switch platform, built around the Quantum-3 ASIC and paired with Blackwell-class GPUs (GB200, B200, B300) over ConnectX-8/9 SuperNICs running at up to 1.6 Tb/s per GPU. The Q3400-RA is the 4U flagship: 144 ports of 800 Gb/s XDR across 72 twin-port OSFP cages, 115.2 Tb/s of non-blocking aggregate throughput, and sub-100 ns port-to-port latency. A smaller 2U Q3200-RA (72 ports, 57.6 Tb/s) covers lower-radix leaf roles or bridges legacy Quantum-2 fabrics into an XDR build. Both chassis run as leaf or spine in a two-tier fat tree, and NVIDIA's own reference design scales a single fat tree built from Q3400-RA switches to 10,368 NICs.
- Quantum-X800 is the fabric to specify for Blackwell/GB200-class 800G endpoints; it is not a drop-in upgrade path for existing NDR fabrics, since cabling and optics are a different generation end to end.
- A documented GTC 2024 reference design builds a 576-GPU rail group as a 'virtual modular switch' from 4 Quantum-X800 switches in a 3-tier topology; treat single-switch radix numbers as a building block for such designs, not a cluster-sizing shortcut on their own.
- The dedicated management OSFP port keeps UFM traffic off the data plane; budget a cable and a port for it even though it does not show up in the headline 144-port count.
- Chassis power draw (2,900 W typical, up to 7,000 W with active cabling on the Q3400-RA) approaches the power budget of a full GPU compute node; rack-level power planning should treat the switch as a first-class consumer, not an afterthought.
How many GPUs can a Quantum-X800 fabric support?
NVIDIA's published two-level, non-blocking fat-tree reference design for the Q3400-RA connects up to 10,368 ConnectX-8 NICs. Actual GPU count depends on topology tier count and oversubscription choices; larger builds add a third tier.
Quantum-2 QM9700 vs Quantum-X800: which one for a new build?
QM9700 runs NDR at 400 Gb/s per port and pairs naturally with H100/H200 and ConnectX-7; it is the mature, widely available choice for 2026 procurement. Quantum-X800 doubles port speed to XDR 800 Gb/s, targets Blackwell-class GPUs with ConnectX-8/9, and is the platform to specify for new 800G-endpoint builds.
Q3200-RA vs Q3400-RA, which chassis?
Q3400-RA is the 4U, 144-port spine-class chassis with 115.2 Tb/s of switching capacity. Q3200-RA is the 2U, 72-port chassis (57.6 Tb/s) built for smaller deployments or for bridging legacy Quantum/Quantum-2 infrastructure into an XDR fabric.
Is Quantum-X800 backward compatible with NDR gear?
Not at the port level. XDR runs 800 Gb/s per port over new OSFP optics and 200 Gb/s-per-lane SerDes, so it requires its own cabling and ConnectX-8/9 endpoints rather than reusing NDR transceivers or NICs.