Trim for Intel® RST and RAID 0 was not supported at all under Windows 8 / 2012 due to some limitations with the Intel® RST driver.
This was fixed in Intel® RST driver release 188.8.131.529, and the latest Intel® RST driver supports Trim for RAID 0 under Windows 8 / 8.1 / 10 and Windows Server 2012. This is natively supported by these OS versions and is normally enabled by default.
However, it is still not possible to run the Optimizer from Intel® SSD Toolbox with Intel® RST in RAID 0, under Windows* 8 / 8.1 / 10 and Windows* Server 2012.
You can find some additional information about TRIM in the following advisory: