Valve made a change to the specifications of the top two versions of the Steam Deck last month, which it seems plenty of people (including me) completely missed. It's not a massive change but still one to be aware of as not all Decks are the same.
The Steam Deck is split across three models either with a 64 GB eMMC, 256 GB NVMe SSD or a 512 GB NVMe SSD (and the top model has the anti-glare etched screen too). Sometime around May 28th though, the SSDs shipping in the Steam Deck changed and now come in two possible editions and you won't know what you have until you get it and check.
On the specifications page, it now lists this:
- 64 GB eMMC (PCIe Gen 2 x1)
- 256 GB NVMe SSD (PCIe Gen 3 x4 or PCIe Gen 3 x2*)
- 512 GB high-speed NVMe SSD (PCIe Gen 3 x4 or PCIe Gen 3 x2*)
With Valve noting "*Some 256GB and 512GB models ship with a PCIe Gen 3 x2 SSD. In our testing, we did not see any impact to gaming performance between x2 and x4".
Really, it shouldn't make all that much of a difference, especially considering the Micro SD slot can load and run even some of the highest-end games just fine. This is quite likely one of the ways Valve has been able to ramp up production to ship more than double each week, along with the two different fan models you might also see.