IOS XE is a release train of Cisco Systems' widely deployed Internetworking Operating System (IOS), introduced with the ASR 1000 series.

[2] It is built on Linux[3][4] and provides a distributed software architecture that moves many operating system responsibilities out of the IOS process[5][6] and has a copy of IOS running as a separate process.

IOS XE is released separately for ASR 1000[8] and Catalyst 3850.

[9] Cisco IOS is a monolithic operating system running directly on the hardware while IOS XE is a combination of a Linux kernel and a monolithic application (IOSd) that runs on top of this kernel.

[10] Another example is the Cisco IOS XE Open Service Containers.