During the Halo Championship Series Invitational, Studio Head Bonnie Ross confirmed that The Master Chief Collection will not be a part of Xbox Play Anywhere. This means that even id you own the collection on Xbox already, you’ll have to purchase it again to play it on PC.
“While MCC shipped before the XPA Play Anywhere, we are exploring ways to make sure that we show our appreciation and recognition for the support we’ve had from the amazing fans on MCCand we’ll have more to announce as we get closer to launch.”– Bonnie Ross
This could mean that while you will have to purchase the game twice Microsoft could be working on a way to transfer game saves between systems. This is another huge feature that won’t be coming to The Master Chief Collection due to the game not being a part of Xbox Play Anywhere. Hopefully this, or some other way to incentivize players to purchase the game on PC after already owning on Xbox is in the works.