Fable Legends will be totally free to play, with the option to purchase in game gold with human monies. The announcement stresses that you won't need that real gold to win; all content in the game will be accessible for free, and you won't be able to 'pay to win' by buying upgrades that are unavailable without real money. Everything that affects gameplay will be earnable within the game.
There's no release date yet set for the game, but there's a good chance it'll come out alongside Windows 10 later this year.