UPDATE: A massive expansion to forge will be coming to Halo 5, this small teaser was found by a user. It gives us a good idea what could come such as race and a sand themed forge map.

 
For the past week or so Halo fans have been speculating what this Voices of War REQ pack is about since it was leaked on the Xbox store. We knew it would contain voices from characters throughout the Halo series, but how would it work and is it free?
These three new voices will work with Warzone, Warzone Firefight and Arena matches. You’ll get access to these three announcers  Spartan Buck, Yabda the Merciless, and 031 Exuberant Witness. This is the first time you are going to have to pay for a new REQ pack, keep in mind this is for fun so you won’t miss out on anything besides the options to change announcers, it will cost $9.99.
They also talked about the upcoming free update that will indeed include the Grenade Launcher from Halo: Reach. They stated “The full bounty of sweet, FREE, content is coming to an Xbox One or PC near you in a matter of days” This means there will be a good amount of forge is this upcoming update since it’s the only thing Halo 5 on PC.

343 will be posting more about this upcoming content update that’s supposedly going to be huge on Tuesday, December 6th.
Source: Halo