SEP 12.1.4 is only version that is compatible for Windows 8.1 and it avaiable in FileConnect.
https://www-secure.symantec.com/connect/forums/sep-121-and-windows-81-blue#comment-9371671
version is: 12.1.4013.4013.
This release provides extended Mac protection, Mac OS 10.9 support, Microsoft Windows 8.1 support, and security improvements, by including the following new features:
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Support for Mac OS 10.9 “Mavericks”.
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Mac IPS protection – Network Intrusion Prevention System based on signatures where each payload in network packet is inspected and compared against a known network attack. If the signatures match, the packet is not allowed to go further in the TCP/IP stack.
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Support for Microsoft Windows 8.1 and Windows 2012 R2.
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Additional Mac client features – New client UI, Update to LiveUpdate 6, Scheduled Scan options parity with Windows, and changes to Mac client packaging to support better distribution via third party deployment tools.
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Mac client support for 4 additional localized languages; Simplified Chinese, Traditional Chinese, Korean, and Brazilian Portuguese.
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SEPM Manageability enhancements – Allowing immediate critical security event notification and additional telemetry.
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Fixes for customer reported defects.
Upgrade and Migration paths
The following Symantec Endpoint Protection Manager versions and Symantec Endpoint Protection Windows client versions can upgrade directly to version 12.1.4:
- From 11.x to 12.1.4 (enterprise version)
- 12.0.122.192 Small Business Edition
- 12.0.1001.95 Small Business Edition - Release Update 1 (RU1)
- 12.1.671.4971
- 12.1.1000.157 - Release Update 1 (RU1), with or without maintenance patches
- 12.1.2015.2015 - Release Update 2 (RU2), with or without maintenance patches
- 12.1.3001.165 - Release Update 3 (RU3)
https://www-secure.symantec.com/connect/blogs/latest-symantec-endpoint-protection-released-sep-121ru4