The latest SED version is 10.4.1, and you can always find this out by going to the Release Details section of the below page:
https://support.symantec.com/en_US/encryption-desktop.html
It's worth noting however, that if your use case is purely for disk encryption, Symantec normalyl recommend using SEE instead (https://www.symantec.com/products/information-protection/encryption/endpoint-encryption).