The module Xbee and Xbee Pro using stack zigbee 2004 or 2006?

The module XBee Series 2 is Zigbee compliant and uses zstack 2007

This is copied straight from page 6 of the ZB OEM guide found here:

The XBee/XBee-PRO ZB firmware release can be installed on XBee ZNet or ZB modules. The XBee ZB firmware is based on the EmberZNet 3.x ZigBee PRO Feature Set mesh networking stack, while the XBee ZNet 2.5 firmware is based on Ember’s proprietary “designed for ZigBee” mesh stack (EmberZNet 2.5.x). ZB and ZNet 2.5 firmware are similar in nature, but not over-the-air compatible. Devices running ZNet 2.5 firmware cannot talk to devices running the ZB firmware.