Reference Liquid-Cooled Radeon RX 6900 XT Listed, Possibly the RX 6900 XTX, with Faster Memory | TechPowerUp
 
To preempt NVIDIA's GeForce RTX 3080 Ti launch, AMD had worked with its partners to release a refreshed Radeon RX 6900 XT based on a swanky new ASIC internally dubbed "XTXH." This is essentially the highest bin of the "Navi 21" silicon that allows 10% higher clock speeds over the standard RX 6900 XT. Our testing of one such card, the ASRock RX 6900 XT OC Formula, showed that the XTXH is able to trade blows with the RTX 3090, making it competitive with the RTX 3080 Ti. Interestingly, there seemed to lack a reference design "made by AMD" card based on this silicon. Turns out, AMD had other plans. This card was earlier believed to be the "Radeon RX 6900 XTX," when it was first leaked in April, but turns out, that AMD is allowing partners to simply call this the RX 6900 XT.

The reference design card uses a liquid-cooled design. The card itself is two slots thick, and about the size of the reference Radeon RX 6800, but two coolant tubes emerge from its top, which head to a 120 mm x 120 mm radiator. This is a purely liquid-cooled card, with no secondary air-based cooling, like the ASUS ROG Strix LC RX 6900 XT. The only sources of noise are the AIO pump-block, and the single included 120 mm fan. Besides 10% higher GPU clocks, the reference design card has an ace in the hole that custom-design XTXH cards lack—faster memory.
 
A listing of a Sapphire-branded reference liquid-cooled card on Brazilian online store Kabum claims that the card comes with a memory clock speed of 18 Gbps GDDR6. Samsung has been mass-producing 18 Gbps-rated GDDR6 memory chips (which are not GDDR6X), since 2018, so it's likely that AMD secured itself some volume to send to its reference-design OEM, PC Partner. At 18 Gbps, the memory bandwidth shoots up to 576 GB/s, from 512 GB/s on the RX 6900 XT.

The card's engine boost frequency is listed as 2435 MHz, which is in the league of other XTXH cards, so it's not like the faster memory is compensating for lower engine clocks. What's interesting, though is that the pictures reveal that the card makes do with just two 8-pin PCIe power connectors—a configuration rated for 375 W—while every custom-design XTXH card uses a triple 8-pin configuration rated for 525 W. Kabum claims the card will ship from 30th June, 2021.
 
I fully expect these to sell out quickly due to demand.