VPN, CISCO AnyConnect, Mac OS X Version compatibility
The current version of the Cisco AnyConnect client available through WebStore (4.3.05017) is officially supported and compatible with Mac OS X versions that support 32-bit applications (Mac OS 10.9 and above) including 10.11 (El Capitan), 10.12 (Sierra), 10.13 (High Sierra).
Is the Cisco AnyConnect VPN compatible with Mac OS X El Capitan (10.11)?
This version is NOT compatible with Mac OS X versions that require 64-bit applications. Mac OS 10.13 is the last version of Mac OS that will support 32-bit applications .