Firaxis has announced that it's celebrating XCOM's sixth birthday on October 9th with the release of the Tactical Legacy Pack - a brand-new (and temporarily free) DLC update for XCOM 2's War of the Chosen expansion on PC.
The Tactical Legacy Pack is designed to bridge the timeline gap between the first Firaxis XCOM game, Enemy Unknown, and its 2016 sequel. It includes new modes, maps, weapons, and armour - all designed to "honour the legacy of the XCOM series".
The centrepiece of the new DLC appears to be the new Central's Archives Legacy Ops campaign. Its consecutive tactical challenges are themed around the recollections of Central Officer Bradford and other key members of XCOM, focussing on events that led to the formation of the resistance between the first and second XCOM games.