XenServer is the product. Xen is the hypervisor. The confusion has lasted nineteen years: XenSource packages Cambridge, Citrix buys it for half a billion, renames it Citrix Hypervisor, private equity restores the name, and in July 2026 XenServer 9 becomes “Citrix” again and supports every kind of workload — not just desktops. This is the story of the appliance, not the paper.
XenSource: the appliance on top of Xen
The free hypervisor was born in Cambridge — its origins are in The history of Xen. What was missing was a product: an ISO, a console, a host pool, users not needing xm. In 2005, XenSource became a company. Anil Madhavapeddy, from the original team, was release manager for the first commercial distribution. The trick was to hide Xen behind a Linux appliance: what the customer saw was “start VM,” not “dom0.”.
The Microsoft partnership began in fall 2006 — VMware was irritating both companies. In August/October 2007, Citrix bought XenSource for US$ 500 million. Steve Wilson (Sun’s xVM) was looking at VirtualBox on the desktop; Citrix wanted servers and VDI. XenServer was born as the “Microsoft-friendly” hypervisor in the Citrix portfolio, alongside XenApp and XenDesktop.
The Citrix era: HA, XenCenter, a true type 1
Type 1, bare metal: Xen starts from the bootloader, CentOS (later) becomes dom0, XAPI speaks HTTP/XML-RPC, and XenCenter (Windows) or xe is in charge. Live migration, pools, storage repositories, HA in 5.0 (OCaml underneath). GPUs, then vTPM for Windows 10/11. For a few years, XenServer genuinely competed with VMware and Hyper-V. By 2014, Gartner already thought Citrix had given up on general-purpose servers and tied itself to its own VDI.
2013: open source and the death of XCP
On June 25, 2013, Citrix announced XenServer 6.2 was entirely open and free — features that had been Platinum no longer required a license. XCP (Xen Cloud Platform), the “almost XenServer” ISO that had existed since 2011, lost its purpose. “XCP is dead; long live XenServer,” wrote the Xen Project. The code moved to xenserver.org. What did not open up: the license daemon, some storage drivers, the closed-source HA.
2018: Citrix Hypervisor and the Free cuts
Citrix’s Xen* line became a single brand: XenServer became Citrix Hypervisor; XenApp/XenDesktop became Virtual Apps and Desktops. In December 2017, 7.3 removed from Free what labs had used at no cost: storage XenMotion, dynamic memory control, GPU passthrough. Security patches for older versions required a contract. It was the spark for XCP-ng.
2022–2026: the name returns, version 9, Citrix again
On September 30, 2022, Vista Equity and Evergreen bought Citrix (US$ 16,5 billion) and merged it with TIBCO into Cloud Software Group. The hypervisor became a separate unit and regained the XenServer name. In March 2024, XenServer 8 came out — essentially Citrix Hypervisor 8.2 CU1 with patches, a three-host trial, and a VMware migration tool. Citrix’s 8.2 reached EOL on June 25, 2025.
In July 2025, Citrix said XenServer was returning to “every kind of workload.” On July 1º, 2026, it launched XenServer 9 (preview, GA during the year): Xen 4.21 hypervisor, a new control domain OS, NUMA, Secure Boot. CSG’s XenServer unit ended; the product returned “under the Citrix umbrella.” Standalone Standard/Premium had already reached end-of-sale in June 2024 — the license now comes within Citrix subscriptions (Private Cloud, Hybrid, Platform).
Timeline
- 2005 — XenSource packages the Cambridge hypervisor as an appliance
- 2006 — Partnership with Microsoft (VDI and servers)
- 2007 — Citrix buys XenSource (US$ 500 million); XenServer is born
- 2008 — HA and pools in XenServer 5.0 (XAPI in OCaml)
- 25/Jun/2013 — XenServer 6.2 fully open; the end of XCP
- Dec/2017 — 7.3 cuts Free features — the spark for XCP-ng
- ~2018 — XenServer is renamed Citrix Hypervisor
- 30/Sep/2022 — Vista/Evergreen buy Citrix (US$ 16,5 billion); the XenServer name returns
- Mar/2024 — XenServer 8
- 1º/Jul/2026 — XenServer 9 (Xen 4.21), under the Citrix brand again
Where it fits
Those who want the same stack without Citrix go to XCP-ng (a “friendly” fork, XAPI intact). Those who want KVM+LXC on Debian, Proxmox. To take an OVA from VirtualBox and land it on XAPI: ova2xva.
XenServer 9, Xen 4.21, with the Citrix logo again. The appliance from 2005 still exists. The name, for the third time, does too.