You can play through the base game and the first two expansions for free but if you wish to free yourself from the F2P account restrictions or play beyond the Stormblood Expansion you will need to pay a monthly subscription but until that point you can play as much as you want and experience over 250 hours of content for free.
And no this isn't going completely free to play any time soon not only is FFXIV Square-Enix's most profitable game right now but they are still charging a subscription fee for FFXI to this day and that game came out in 2002.