As per an ECC listing uncovered by @Komachi on Twitter, AMD may be working on a non-XT variant of the Radeon RX 6900 XT. The file is from ASUS which includes the TUF, ROG Strix, and Dual variants of both the RTX 30 series parts as well as the Big Navi GPUs, plus this mysterious RX 6900.
In my personal opinion, this is a typo as there’s already not much of a performance delta between the 6800 XT and the 6900 XT. While the former packs 72 CUs or 4,608 shaders, the latter comes with 80 CUs or 5,120 shaders. That results in a single-precision performance delta of just over 2 TFLOPs. In comparison, the RX 6800 and 6800 XT have an FP32 compute gap of nearly 5 TFLOPs.
This is because of the fact that the former not only has fewer CUs (60 vs 72), it also has a lower core boost clock (2,105MHz vs 2,250MHz). This results in the RX 6800 XT being approximately 15-20% faster than its non-XT sibling. In contrast, the RX 6900 is going to be only ~10% faster than the RX 6800 XT if we consider the spec difference. Having a 6900 (non-XT) that’s just 5% faster than the 6800 XT would be as redundant as having a 6800X between the 6800 and the 6800 XT.