AMD RX 6900 XT review

After years of waiting, Big Navi is finally here: the AMD Radeon RX 6900 XT. A high-end enthusiast graphics card that existed solely in the hopes and dreams of enthusiasts for over a year—and in the Radeon Technology Group labs for surely much longer—the RX 6900 XT is the ultimate expression of the RDNA 2 architecture.

A known quantity since October, the RX 6900 XT will be a familiar sight for anyone that read our RX 6800 XT review. It features the same triple-fan cooler design, memory configuration, and even TGP and clock speeds as the RX 6800 XT. Hence why plenty of what I spoke about back in November regarding the impressive updates to the RDNA 2 architecture is still valid in regards to the more expensive $999 card.

But the RX 6900 XT takes aim at Nvidia's GeForce RTX 3090, a Titan in all but name, and you'd be right in thinking something must've changed to get anywhere close to realising that lofty goal. There has been one key change to the hardware: Where the RX 6800 XT includes 72 compute units (CUs) for a total of 4,608 stream processors, the RX 6900 XT comes with 80 CUs and 5,120 stream processors.

And I have to say the prospect of a card that comes close to Nvidia's $1,499 graphics card for two-thirds of the price had me excited for a long while. All the amped-up marketing from AMD's 'Where Gaming Begins' worked its magic on me, and any fears I perhaps should've had for a $1,000 graphics card lodged unceremoniously between the RTX 3080 and RTX 3090 melted away like soft-serve on a hot day.

Specifications

What are the AMD RX 6900 XT specs?

The AMD Radeon RX 6900 XT specs sheet is as fully-loaded as it gets. But let's start with the core ingredient: RDNA 2.

As I mentioned previously, if you want a more detailed rundown of AMD's brand new RDNA 2 architecture, you need only look to our RX 6800 XT review's architecture section. There are a lot of improvements over the first generation RDNA gaming architecture to talk about, which likely demands its own deep-dive, but for now, let's focus on the specifics of the RX 6900 XT's implementation.

The same Navi 21 GPU resides within the Radeon RX 6900 XT as the two RX 6800-series graphics cards we've already reviewed, meaning you're getting an identical, and very effective, dual compute unit configuration that's tailor-made for gaming—albeit on a slightly larger scale with the 80 CU RX 6900 XT. That makes for a total of 5,120 stream processors—an 11 percent increase over the RX 6800 XT.

That comes with a price increase, too. The RX 6900 XT is priced at $999, whereas the RX 6800 XT is available (if you can find one in stock) for $649. Both the RX 6800 XT and its little sibling, the $579 RX 6800, are largely unavailable right now, however. We suspect the launch of the RX 6900 XT to go much the same way, if not be more sparsely available as most high-performance GPUs tend to be manufactured at lower quantities.

If you can get your hands on one, you'll be gifted an incredibly well thought-out architecture, with enhancements to clocks and power delivery ensuring the core GPU is running like a well-oiled machine. Even with a high core count and TGP in line with the RX 6800 XT, the RX 6900 XT easily breaches 2.2GHz clocks under load.

To enable such a chip to operate within the same 300W TGP as the RX 6800 XT, AMD is employing a handful of other optimisations for every Navi 21 GPU destined for the RX 6900 XT. A binning process ensures the Navi 21 GPU within the RX 6900 XT is one of the best samples out of TSMC's 7nm fabs, and each one has been carefully selected for its ability to meet performance requirements while retaining power efficiency. 

There's also a minimum VRM power delivery requirement for all RX 6900 XT graphics cards, with the reference AMD model offering 16-phase VRM power delivery. That, AMD says, is the key to maintaining similar wattage to the lower-spec model while maintaining greater performance. That and the binning, of course. 

And yes, that is confirmation that there will be third-party models of the RX 6900 XT. These will arrive shortly after launch. For now, however, the RX 6900 XT will only be available in reference garb, the exact same heatsink and cooler design found on the RX 6800 XT. That's one way that the RX 6900 XT has the RTX 3090 immediately beat, too, it's nowhere near as huge. Yet it is still plenty capable of managing the heat produced by that 519 mm2 GPU, running slightly hotter than the RX 6800 XT under load at 74°C, to the second-tier card's 68°C.

Perhaps the most noteworthy function added with RDNA 2 is ray tracing capability, however, made possible by the inclusion of AMD's Ray Accelerators. 

These Ray Accelerators are dedicated ray-tracing hardware acceleration blocks fused next to the traditional rendering pipeline. There's one Ray Accelerator for every CU, and so the RX 6900 XT comes with the most ray tracing silicon of the lot at 80. These blocks are specifically designed to accelerate the BVH (bounding volume hierarchy) traversal step, which would usually be a far too compute-heavy step for a GPU without acceleration, as we've seen with 16-series and 10-series ray tracing on older generation Nvidia GPUs.

The remaining steps are carried out on the traditional shader units within the GPU. That's unlike Nvidia's dual RT Core and Tensor Core approach with Ampere, which divvies up denoising to the AI-inference accelerating Tensor Cores. As such, much to the same result as with the previous two RX 6000-series launches, AMD's approach is a little off the pace of Nvidia's RTX 30-series—even the $399 RTX 3060 Ti isn't all that far behind the RX 6900 XT in 3DMark's brand new DirectX Raytracing Feature Test.

But the RX 6900 XT has a significant leg up over the competition in other ways to make up for it. A seriously capacious 16GB of GDDR6 memory helps the RX 6900 XT at least despatch fears of some future VRAM hog eating up all your buffer. That's fed by the same 256-bit memory bus as the other cards, yet as we know that's not quite the end of the story with RDNA 2.

AMD's secret weapon for its high-performance GPUs is its Infinity Cache, a feature it plucked in spirit from its AMD EPYC server chip cache subsystem, and subsequently chopped and changed over the course of a few years before finally unleashing it within the Navi 21 GPU.

We're once again looking at 128MB of Infinity Cache with the RX 6900 XT, the same found with all RX 6000-series cards so far, and that which AMD touts as enough to successfully prevent a slower call to external memory some 60-80 percent of the time. That's all without dramatically increasing die size, cost, or power requirements, it says.