Creed begins a new chapter in the Rocky universe.
I wouldn't call it a full reboot, but imagine your IT department removed all of the burdensome Rocky franchise cookies, malware and viruses. Of course, I'm speaking of Talia Shire porn.
In the new Creed universe, Rocky still beat Ivan Drago's ass and singlehandedly ended the Cold War, but Rocky V is probably no longer canon and the scene in Rocky III where Rocky smokes Apollo in a beach sprint after a 6 week training camp in Watts would likely be explained by Apollo having a bunion.