Some staffers from 2K Marin, devs on The Bureau, held an Ask Me Anything on reddit an hour ago, and despite the fact that a lot of folks tend to tie the identity of the XCOM franchise to a gameplay genre that this prequel is looking to skirt a bit, there was a question about the canonicity of next week's title.
So how does The Bureau tie into the XCOM saga? That is yet to be firmly established, said lead narrative designer Erik Caponi in response to a question about whether it is connected with Enemy Unknown 2012 at all.
"The Bureau is the origin story of the XCOM organization. So, the short answer is 'as far as we know'. Although we're talking about a setting that has time and space bending aliens, so the answer to that may ultimately turn out to be less clear.
"But lets go with yes. For now."
That said, there are references to later XCOM things in The Bureau, as Caponi described at another point in the thread.
"In tying the menagerie of XCOM species together, we had to have a reason for them to be fighting side by side. In this case, the Zudjari are a conquering species, searching for a new planet to settle on. They have failed so far, and have bounced from world to world, conquering and stripping planets of their resources before moving on. In some cases, they were able to enslave a number of species and conscript them in the their forces. This is the case with the Sectoids and Mutons. The bridge we built there was to drop hints of what happens to those species after the events of our game to the point where they show up in later XCOM titles.
"In addition to that, some of the technology from 60+ years later shows up in an early form in our game. We've shown the Sectopod, which is effectively a prototype of the more powerful one we see in Enemy Unknown. Looking at the redesigns of those enemies and imagining what earlier and less advanced versions would look like was fun and challenging."