Rare AMD Ryzen 9 5900X3D Engineering Sample Surfaces With 128 MB L3 Cache
A rare unreleased AMD Ryzen 9 5900X3D engineering sample has surfaced online, giving PC hardware enthusiasts another look at AMD’s experimental 3D V Cache work on the AM4 platform. The sample was posted by Chiphell user Reiuji Utsuho in a Chiphell forum thread, showing what is presented as a 12 core and 24 thread Ryzen 9 processor that was never released to consumers.
The confirmed details from the shared images and post are limited but notable. The chip is identified as an engineering sample, it is shown as a Ryzen 9 class Zen 3 CPU with 12 cores and 24 threads, and the reported cache figure is 128 MB of L3 cache. That immediately separates it from the retail Ryzen 9 5900X, which launched with 64 MB of L3 cache, and from the retail Ryzen 7 5800X3D, which became AMD’s main AM4 gaming processor with 96 MB of L3 cache.
The internal cache layout has not been officially documented by AMD, but the reported figure points to a clear technical explanation. A standard Ryzen 9 5900X uses 2 Zen 3 CCDs with 32 MB of L3 cache each. With 128 MB total L3 cache, the most straightforward reading is that 1 CCD received the extra 64 MB 3D V Cache stack, creating a 96 MB cache CCD paired with a normal 32 MB CCD.
That layout would place the sample between the retail Ryzen 7 5800X3D and AMD’s earlier dual CCD 3D V Cache demonstrations with 192 MB of total L3 cache. It would also make the chip conceptually similar to later dual CCD Ryzen X3D processors, where 1 chiplet carries the larger cache pool while the other remains focused on clock speed and general compute behavior.
The post also shows the sample boosting close to 4.65 GHz in monitoring software, placing it near the retail Ryzen 9 5900X, which officially boosts up to 4.8 GHz. The BIOS behavior is more limited, with the Chiphell post indicating that the sample depends on older firmware support and does not behave like a normal retail CPU. That fits the nature of an engineering sample, which is typically used for validation, internal testing and platform experiments rather than direct consumer release.
This leak arrives at an interesting moment for AM4, we know the AM4 Is Still Getting Fresh BIOS Updates Nearly 9 Years After A320 Arrived, the platform continues to receive firmware support long after most desktop sockets would have faded from relevance. Seeing an unreleased Ryzen 9 5900X3D sample appear now is a reminder that AM4’s long life included far more internal experimentation than the final retail lineup revealed.
The Ryzen 9 5900X3D engineering sample is compelling because it shows how far AMD explored AM4 before settling on the Ryzen 7 5800X3D as the platform’s defining 3D V Cache gaming processor. A 12 core Zen 3 chip with 128 MB of L3 cache would have appealed strongly to users who wanted more cores than the Ryzen 7 5800X3D while still gaining the gaming advantages of stacked cache.
The tradeoff was likely complexity. A mixed CCD design would have required careful scheduling, BIOS validation and clock behavior tuning, especially for games that needed to land on the cache heavy chiplet. AMD probably made the cleaner retail choice with the single CCD Ryzen 7 5800X3D, but this sample shows that a more ambitious 12 core X3D path existed inside the AM4 era.
Would you have bought a 12 core Ryzen 9 5900X3D for AM4, or was AMD right to focus on the simpler Ryzen 7 5800X3D design?
