An engineering sample of AMD's cancelled Ryzen 9 5900X3D has appeared on the Chiphell forums. The 12-core Zen 3 chip carries 128MB of L3 cache, twice that of the standard Ryzen 9 5900X, because AMD stacked 64MB of 3D V-Cache onto one of its two CCDs. The sample's CPU-Z screenshot shows a boost clock around 4.65GHz, close to the 5900X's 4.8GHz.
AMD had already shown a 12-core 3D chiplet prototype at Computex 2021, claiming up to 15% higher average gaming performance than a 5900X at a fixed 4GHz. The company also experimented with 192MB L3 configurations by putting V-Cache on both CCDs of 12-core and 16-core chips. Those dual-stack parts were apparently considered, but they introduced cross-die latency and lower clocks due to thermal and power limits.
AMD ultimately shipped the 8-core Ryzen 7 5800X3D with a single V-Cache CCD, a design that proved strong for gaming. According to Tom's Hardware, later dual-CCD X3D parts, such as the Ryzen 9 9900X3D and 9950X3D, still trail the 8-core Ryzen 7 9800X3D in gaming, supporting AMD's decision to keep gaming-focused chips on one CCD.