XENPAK is a multisource agreement (MSA), instigated by Agilent Technologies and Agere Systems, that defines a fiber-optic or wired transceiver module which conforms to the 10 Gigabit Ethernet (10GbE) standard of the Institute of Electrical and Electronics Engineers (IEEE) 802.3 working group.
The result covered all physical medium dependent (PMD) types defined by the IEEE at that time for 802.3ae 10GbE.
[1] Although the XENPAK agreement received early support, its modules were thought to be overly large for high-density applications.
Newer XENPAKs using the 10GBase-LX4 standard operated using multiple wavelengths on legacy multi-mode fibers at distances of up to 300 metres (980 ft), eliminating the need to reinstall cable in a building when upgrading certain 1 Gbit/s circuits to 10 Gbit/s.
The XENPAK form factor was initially supported by numerous network equipment manufacturers and module makers.