That is right! Free content in the form of REQ pack DLC is available to Halo 5: Guardians owners! The DLC contains the Challenger armor set and HaloWC emblem. You can proceed to the Xbox store to obtain your copy here.
However, the pleasant surprises don't stop here as the developer team has also released a trailer featuring the Warzone Firefight gameplay. Warzone Firefight is a mode that has been in development for some time. The mode has been teased in February. In case you have missed the reveal, you can see February trailer below.
And here you can find a trailer that was released today, to celebrate Halo World Championship finals: