Heres my conversation with xbox live service rep
You are now chatting with ‘Miranda’.
Scott: Hi
Miranda: Hello, thank you for contacting Xbox Customer Support. My name is Miranda how can I help you today?
Miranda: Hi Scott, how are you doing today?
Miranda: I hope everything is just fine.
Scott: i just want to know about the Halo 4 specalization code, everyone who played halo 4 before the 20th got one. i have not
Miranda: Oh! Let me check on that one for you.
Miranda: Indeed we send codes to everyone who played Halo4.
Miranda: And our Team has started to sent out codes yesterday for the first batch.
Miranda: Let me arrange this for you, Scott.
Scott: okay, what do i need to do?
Miranda: Please give me a moment I’ll tap my team and check your account here.
Scott: alright
Miranda: I have a great news to you.
Scott: whatsup?
Miranda: You will get one.
Miranda: That’s an assurance.
Scott: okay
Miranda: They send it by batch, and you belong to the next batch.
Scott: alright when will that go out?
Miranda: They will send out codes up until December 3,2012 Eastern Time.
Miranda: How’s that sound? 
Scott: that sounds good, your positive?
Miranda: Very, and I am confident.
Scott: im guessing you guys have had alot of questions on this?
Miranda: I myself belongs to the next batch to receive the code.
Miranda: I ma viewing your account right here, and the lists of qualified Xbox Members.
Scott: one quick question
Miranda: Please check your email address (aim.com)
Scott: can u tell me what email it will be?
Miranda: Sure, go ahead.
Scott: ------------@aim.com yes?
Miranda: That’s right.
Miranda: Sure, you are most welcome and valued.
Miranda: Would there be anything else that I may check for you?
Miranda: Are we satisfied with the service provided today. Just making sure though before we end.
Scott: yes
Miranda: That’s what we have here attached on your GT. 
Scott: alright thank you very much
Miranda: Thank you for seeing the effort.
Miranda: Worry not. You can have my word.
Miranda: Thanks for contacting Xbox Customer Support and have a great day!
from this i have learned there is a second batch going out and evryone eles will get one before december 3rd
so if you havent recived yet, hang in there! i was worried at first too