When will come out avatar book 4 or is through 3 the last chapter of avatar?

The Avatar: The Last Airbender story is considered to be complete with the three seasons.

However, the Avatar universe continues! Here's a breakdown:

* Avatar: The Legend of Korra: This series, set 70 years after the original, follows the next Avatar, Korra, and her adventures. It has four seasons and is also considered a complete story.

* Other Media: The Avatar universe has expanded through comics, novels, and video games, offering further adventures within the world.

So, while the original Avatar: The Last Airbender is finished, there's plenty more Avatar content to explore!