Diablo IV developers confirm that Direct Storage technology is not yet active in the game
The Diablo IV development team has confirmed that despite the fact that Direct Storage files are present in the game, it is not currently active - the developers plan to add the technology in the future.
Here's What We Know
Back during testing in March, there were reports that Direct Storage and DLSS files were found among the game's files. However, since then, there have been no further reports of their implementation, leaving Forspoken as the only game to actually use Microsoft's SSD technology. This is the only visible application of this technology in Forspoken.
Flashback
DirectStorage is a technology that enables games to make efficient use of the power and performance of SSDs, particularly those running the high-bandwidth NVMe protocol. Previously, due to the use of conventional hard drives in many systems, including consoles, developers had to take into account the slowest component of the system.
Source: PC Gamer