Cisco Cisco IOS XE 3.5E

As 

 shows, each version of Cisco IOS XE has an associated Cisco IOS version:

If you are upgrading to Cisco IOS XE Release 3.8.xE and plan to use VSS, you must upgrade your 
ROMMON to IOS Version 15.0(1r)SG11.

ISSU is supported on 4500X in VSS configuration.

If dual supervisor engines are present, first upgrade your software to Cisco IOS XE 3.2.0SG or later, then 
upgrade your ROMMON to IOS Version 15.0(1r)SG7 to avoid an uplinks issue (CSCtj54375).

VLAN Switching and Selective QinQ 
on the Same Port 

Option to disable default behavior of dropping non-translated VLANs. When 
configuring VLAN mapping for selective Q-in-Q on a trunk port, you now have the 
option to specify that packets that do not match, should not be dropped (Enter the 
no switchport vlan mapping default drop command).

(IP Base, and Enterprise Services)

VRF-aware WCCP for IPv4 traffic

WCCP now supports IPv4 traffic redirection to and from Virtual Routing and 
Forwarding (VRF) interfaces. 

(Enterprise Services)

VRF-aware WCCP for IPv6 traffic

WCCP now supports IPv6 traffic redirection to and from Virtual Routing and 
Forwarding (VRF) interfaces. 

(Enterprise Services)

VSS

The REP, Flexlinks, Unidirectional Link Detection (UDLD), and Fast UDLD 
features are now supported on VSS.

(IP Base and Enterprise Services)

WCCP Version 2 for IPv6

WCCPv2 now supports IPv6 traffic.

(IP Base and Enterprise Services)

03.3.0SG

15.1(1)SG

03.3.1SG

15.1(1)SG1

03.4.0SG

15.1(2)SG

03.5.0E

15.2(1)E

03.6.0E

15.2(2)E

03.7.0E

15.2(3)E

03.8.0E

15.2(4)E