It's free yeah? For the entirety, you don't need a month's sub or anything
I know on PC there is a free trial that lets you play for an unlimited amount of time, but has a pretty limiting feature set. For the story, it extends through the game's second expansion now, I believe. However, you can't form a party (you can be invited into other players parties, and you can do dungeon raids that auto-create parties), you're capped at level 70, you don't have access to most of the advanced jobs, and you also can't use the marketplace to buy things from other players. This last one gets cumbersome quickly as you can still buy most things from NPCs / shops in the game, but they're very spread out and cost more than the typical "market price" for most things.
Unclear if this free trial will extend onto Xbox or not. It is available on PlayStation, so I would guess it's probably also going to be available on Xbox.
One thing to note - once you upgrade from the free trial to the full game / paid subscription, there is no going backwards. Even if your character is under the level cap, hasn't gotten very far in the story, etc., there is no way to "downgrade" your account to the free trial and you'll have to pay the monthly subscription to keep playing.
