This bizarre cult has whipped up a religious frenzy following the appearance of the Dimensional Gates. The cult has long believed in redemption of the human race by a superior Alien race. They believe the UFOs and Aliens to be harmless and are rapidly gaining credibility and recruits from the general populations. This represents a considerable threat to X-COM because the cultists will do anything to assist the Aliens in their purpose, whatever that might be."
While at first they may seem similar, and EXALT could still be written as the precursors to the Cult of Sirius, one operational difference between the two groups is that the religious structure of the Cult speaks of humans subjecting themselves to their new alien overlords, while the extravagance of the EXALT Headquarters suggests powerful people in Black Market and clandestine circles, groups who's interest tend to lie in accuiring power for themselves.