Many fans think he is, though it's never been officially confirmed (obviously). However, the main reason why they believe Chuck is God is because of the last time we saw him - he disappears (while wearing white clothes) in a way we've never seen any creature do. Also by the way he was narrating the "end" of the Book of Winchester implies that creating a good ending is hard even for him.
So the hints point to yes, he is God. Of course, I'm sure this is something that the writers will never confirm and leave to fan speculation forever.
I think Supernatural will stop short of the 'upper-ranks', no God, no Satan, no Jesus(they moved close a couple of times, but always stopped short), they're probably scared it'll turn the show into a political-tool, which is a very real risk.
It's never been confirmed, but a lot of the fans think he is. It makes sense because he writes those books about the Winchesters before any of the things that occur in the books actually happen to them.
I think he really might be. It was weird how the first time we saw him he disappeared in that white light at the end... what was that? (p.s. I've only ever watched up to season 8 so idk if anything else about Chuck has occurred)
I have been debating this over and over for some time but is Chuck God?
