In a rather unexpected discovery, it was found that the Xbox Series S features a replaceable SSD, in M.2 2230 form factor. The limited storage of the Series S has been one of the most controversial topics in the Xbox community. The budget console features a 512GB NVMe (PCIe 4.0 based) drive, part of which will be used by the OS and other first-party software, bringing it down to around 450GB.
In comparison, the Xbox Series X which features a 1TB NVMe SSD features a soldered drive.
Update: Both the consoles feature removable SSDs, but there’s likely an authenticity check in place:
Although, there’s an option to expand the storage using an add-on card, that comes in at around $200 for the 1TB variant, nearly half the price of the console.
It’s unlikely that Microsoft will let users simply replace the SSD as you do with a PC. There will likely be authentications or device verification put in place by the design team, and there’s also the matter of the OS. It may be difficult to move it to a third-party drive without failing any checks. Regardless, it should make replacements cheaper and more convenient.