i was scrolling through reddit and found this. someone has looked into the source for halo 5 and found this.
Found these “Spartan Company Messages” which seem to indicate that a clan system is planned for Halo 5:
Clan_Join_Request_Subject= Seeking enlistment into {clan}; Clan_Join_Request_Default_Body= {gamertag} is seeking to enlist in {clan}; Clan_Join_Request_Accepted_Subject= Welcome to {clan}; Clan_Join_Request_Accepted_Body= Congratulations, {gamertag} you’ve been accepted into {clan}; Clan_Join_Request_Rejected_Subject= Your request for enlistment has been rejected.; Clan_Join_Request_Rejected_Body= Sorry, {gamertag} your request for enlistment into {clan} has been rejected. Keep practicing and get those stats up!; Clan_Invite_Request_Subject= {clan} is requesting you to show up for duty; Clan_Invite_Request_Default_Body= Congratulations, {gamertag} you’ve been invited to enlist in {clan} for service; Clan_Promote_To_Lieutenant_Subject= You have been promoted to Lieutenant; Clan_Promote_To_Lieutenant_Body= Congratulations, {gamertag} you’ve been promoted to Lieutenant! Please review this list of duties expected of you.; Clan_Demote_To_Member_Subject= You have been demoted from Lieutenant; Clan_Demote_To_Member_Body= Sorry, {gamertag} you’ve been demoted and your services as Lieutenant will no longer be required.; Clan_Discharge_Member_Subject= You have been dismissed from {clan}; Clan_Discharge_Member_Body= Sorry, {gamertag} you’ve been dismissed from {clan}, your services will no longer be required.; Clan_Deleted_Subject= {clan} has been disbanded; Clan_Deleted_Body= Sorry Spartans, {clan} has been disbanded. You are free to enlist with other Spartan Companies.; Clan_Suspended_Subject= {clan} has been suspended; Clan_Suspended_Body= Sorry Spartans, {clan} has been suspended and is now considered inactive. We expect you to all work together to resolve the problem.; Clan_Activated_Subject= {clan} has become active; Clan_Activated_Body= Congratulations Spartans, {clan} is now an active Spartan Company. You are now ready to fight the good fight with your other Spartans; Clan_Promoted_Leader_Subject= You have been promoted to Spartan Company Leader; Clan_Promoted_Leader_Body= Congratulations, {gamertag} you’ve been promoted to Spartan Company Leader. Please review this list of duties expected of you.; Clan_Change_Leader_Subject= You have a new Company Leader; Clan_Change_Leader_Body= Attention Spartans, you’ve been assigned a new Spartan Company Leader, {gamertag}. You are expected to serve them as you did the leader before them. Be diligent, be brave, fight the fight, together.;
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Interesting, 343 hasn’t talked about that yet, maybe we’ll see it when they show customs and forge which are more community oriented modes
We picked up this a few months back, but nobody seemed too interested in it. Guessing we’ll find out more closer to launch / when 343 are ready to talk about it 
WHAT! Is this for real??? I have been asking for a clan system for 10 years, and now finally we might get one!?? I can NOT be any more hyped for Halo 5!!
Maybe this is the reason why i haven’t got any response when directly asking basically everyone at 343 about considering adding a clan system. They’re keeping it on the down down low
It’s pretty obvious that 343i isn’t completely overlooking the existence of clans within the Halo community. While it wasn’t a feature-rich clan system like what was present in H2, they did go out of their way to insert a “Clan Tag” in the MCC which is still more than what we ever got from another Halo in these 10 years. While I was disappointed the MCC didn’t have a Clan System, I was still hopeful and just explained that away as 343i simply not wanting to spend the resources on a Clan System for the one-off entry before the main entry.
Very hopeful for this in H5G! I want me some cla…er, Companies 
Halo 2 Had a Clan system lol