343's Bravo gave us the details of today's Halo 4 Matchmaking update.

Bravo MLG -

Today's Halo 4 Matchmaking update welcomes an encore of Spartan Ops Episode 7, as well as several War Games updates.
Premiering this week is the Community Forge Island playlist, which brings with it 6 new community-made maps on Forge Island. It will be available for a limited time only (until the June 3rd Matchmaking Playlist Update). If you haven’t yet downloaded the free Forge Island canvas, head here to download to your Xbox 360. The Community Cartographers have worked hard to select some of their favorite map and game type combinations:
Map: Elevated by Smexi Bilzo
Infinity Slayer
Capture the Flag - 5 Flag
Extraction 1-Site 

Map: Crucifix by Wraith2098
Capture the Flag - 5 Flag
King of the Hill
Infinity Slayer 

Map: Onyx by Hahkarazy
Throwdown v3 Slayer
Throwdown Capture the Flag – 5 Flag
SWAT 

Map: Confined by Big Papa Salot
TD Slayer Pro
Team Snipers
Capture the Flag - 5 Flag 

Map: Ender by The Fated Fire
King of the Hill
Infinity Slayer
SWAT 

Map: Forgotten by Flying Shoe ILR
Extraction 1-Site 
Capture the Flag - 5 Flag
King of the Hill
Please remember to head to the War Games Feedback section and give us your thoughts on the maps and playlist overall. The Community Cartographers and Forgers will review the feedback prior to selecting which of these fine maps will potentially make their way into Halo 4’s official playlists in future updates.
In addition, Big Team Infinity Slayer and Infinity Slayer have some updates as well. 

Big Team Infinity Slayer:
Slayer Pro added to voting options.
Complex added to map rotation.
Voting options reorganized to provide increased variety.
Infinity Slayer:
Slayer Pro added to voting options.
Complex removed from map rotation.
Voting options reorganized to provide increased variety.
We hope you enjoy the new playlist and updates, and we'll see you on the virtual battlefield.