Ryzen 9 9950X3D tops out at 24 lanes

Consumer desktops can host multiple GPUs, but they do not behave like workstation platforms once you start stacking cards. AM5 gives you enough flexibility for one or two serious GPUs; after that, you are fighting chipset uplinks, slot sharing, and PCIe contention rather than scaling cleanly.

• –AMD lists the Ryzen 9 9950X3D with 24 usable PCIe lanes, so there is no hidden lane pool waiting for a 3rd or 4th card.
• –On the ProArt X670E-Creator WiFi, the first two x16 slots can run x8/x8, while the third slot is chipset-attached PCIe 4.0 x16 physical but only x2 mode and shares bandwidth with M.2_3.
• –A Radeon PRO W7800 is a 32GB card with 576 GB/s of local memory bandwidth, not 48GB or 864 GB/s; that bandwidth does not add together across cards.
• –Multi-GPU LLM inference over PCIe can work, but performance depends on interconnect traffic and model partitioning, so throughput usually falls well short of linear scaling.
• –For 300B-class workloads, this is a budget workaround, not a clean future-proof plan; Threadripper or EPYC is the platform that actually matches the hardware ambition.