You Need the Fallout 4 1.6 Update to Play
Another quick note about the release.
Bethesda recently pushed out a 1.6.9 update for PC, Xbox One and PlayStation 4. It's a substantial update for all three platforms.
The 1.6 update delivers support for "Upcoming Add-ons" and that translates to support for the Vault-Tec Workshop DLC.
You need the Fallout 4 1.6 update to play/run the Vault-Tec Workshop DLC on your system of choice so you'll want to get that installed if you want to play the DLC ASAP.
Bethesda recently released a follow-up to 1.6 so you'll also encounter the Fallout 1.7 update if its been awhile since you fired up your system and Fallout 4. This update is require for Bethesda's sixth and final Fallout 4 DLC add-on.