If Sxsi requires network access (licensing, remote data):

On Windows 10 x64, SxS operates through two primary components: manifests and the SxS store (typically located in C:\Windows\WinSxS). The WinSxS folder is notorious for its large size, but this is by design: it stores multiple versions of the same assembly, each in its own subfolder, allowing applications to request exactly the version they were tested with.

Scenario A: Your system runs normally, and sxsi x64 uses 0-5% CPU sporadically.
Do nothing. It is working correctly.

Scenario B: Your computer is slow, and sxsi x64 is constantly consuming resources.
Run DISM /RestoreHealth, then sfc /scannow. Reboot. Install pending Windows Updates.

Scenario C: You suspect malware because sxsi.exe is in a strange folder.
Run a full antivirus scan offline. Use Process Explorer to verify the digital signature.

Scenario D: You want to delete the WinSxS folder to save space.
Stop. This will break Windows. Use the DISM cleanup commands instead.

Sxsi X64 Windows 10