Starting with version 4.02, Sandboxie fully supports Windows 8 without qualifications on both 32-bit and 64-bit editions.
To download version 4.02 or a later version, please visit the Download Sandboxie web page.
With version 3.76 and earlier, Windows warns that Sandboxie v3 is not compatible with Windows 8. This warning applies to versions of Sandboxie before 3.72. When using Sandboxie version 3.74 or later, you can safely disregard the warning message from Windows 8.
Note that Sandboxie offers limited protection in 64-bit Windows 8 compared to earlier 64-bit versions of Windows. In particular, the Experimental Protection feature cannot be enabled and is not available as part of Sandboxie on Windows 8.