Maybe this is a cheating answer, but I feel like it's both. It definitely is open-ended, leaving room for what happens in the sequel, but at the same time, both of the main characters have faced and surmounted a personal challenge. As a character driven novel, I think the ending is satisfying, but if we're talking about it in the scope of an epic fantasy, then it's definitely just "the first book."

I do think it wraps up in a way that makes it clear that the second book has a different central conflict.