The third DLC for Fallout 4, Far Harbor, was released today on all platforms and in all regions. Far Harbor features the largest landmass for an add-on that Bethesda Game Studios has ever created. Filled with new faction quests, settlements, lethal creatures, and dungeons, the new DLC lets you investigate a new case from Valentine’s Detective Agency. Read the official announcement to know more about the content, and If you have any problems starting the DLC's quest line, visit this developer guide.
If you haven't purchased the DLC yet, use these links:
The Xbox store
The PlayStation store
Lastly, listen to Bethesda's employees describing the Far Harbor DLC: