Update:
At least on Steam, the update is a 12GB download.
Original Story:
As detailed yesterday, Doom is getting Free Update 2 and its first ever Double XP weekend today. Before either of them arrive though, Bethesda and id are taking Doom’s servers offline for three hours of maintenance from 9am PT/12pm ET to 12pm PT/3pm ET.
Full patch notes aren’t available for the new Doom update yet, but here’s a look at what we know is included so far:

Doom Free Update 2
New Multiplayer Modes

Exodus is a one-flag capture-the-flag mode with an added twist of constantly moving bases and flags.
Sector is an objective-based capture-and-hold mode where players compete to take control of zones and then hold them to score points.
Both modes can be played on any existing or future maps.
SnapMap

Customizable weapon wheel functionality ? so players can carry and select multiple weapons, just like the campaign
Jump pads with logic to set distance, speed and direction
30 brand-new Hell-themed modules
An expanded weapon list
A new playable demon ? the Mancubus
Improvements to the Community HUB, editor and logic capabilities

General

Tons of optimizations and improvements

The Double XP weekend will begin today as soon as the maintenance ends at 12pm PT/3pm ET.
Next week, id will release Unto the Evil, the first paid multiplayer DLC pack. Priced at $14.99/£11.99/?14.99, it includes three new multiplayer maps, the Harvester demon, the UAC EMG Pistol weapon, the Kinetic Mine,...