According to this Xbox Store page listing, Halo 3: ODST will be making its way to the Master Chief Collection Friday, May 29th. The official listing states,

http://www.drmgamecast.com/2015/05/halo-3-odst-coming-to-master-chief.html

I have never even played ODST so really excited to be getting this.

Halo 3 ODST is now available for download!

Does it come in the form of an update? Haven't touched mcc in a while... Probably still won't. Just too many things to do in the witcher 3...

ironmanDX said: Does it come in the form of an update? Haven't touched mcc in a while... Probably still won't. Just too many things to do in the witcher 3...

I got a messege in my Xbox Live inbox saying it was released with a code to redeem.

Downloading this tonight!!

MCC is the best game deal ever :).

My download has started, this collection is insane.

Yea, hands down the best collection ever.

I wish I had an xbox one :P this would be the first game I would get (I might get one when halo 5 comes out if I have any money xD)