Yea, this question has gotten me confused. The ARG where we decode stuff and get fragments.
How far is it canon.
Well, there are references to things like War Games and Spartan Ops, so finding glyphs on Requiem is canonical, yes.
I’m not up to date on the story of it, but I’d think all the stuff about the AIs is canon too. Not unlikely there are other or more personal AIs aboard Infinity working with the Spartan Ops Teams.
it is completely canon afaik, since stuff found in ARG effect in game (armors/logos/etc)
As stated by Dtape, as far as I am aware the entire ARG and the events that happen within are considered canon events.
You can head to the Section-3 website to get some updates on the storyline, characters, etc in general.
You can also join us in the Halo 4 ARG IRC channel if you’d prefer to speak with operatives console to console and get more personal information and have questions answered directly. 
Almost anybody with the Classified Section-3 forum badge can help you with matters pertaining to the ARG! Just ask! :]