Does Hajime Isayama have an ending in mind for Attack On Titan?

Question

I have read somewhere that Isayama already knows the final ending of the Attack on Titan manga, but the route which he will get there is unknown to him.

Are there any interviews where he specifies this?

Answer 1

There are high chances that the answer is Yes.

He does have an ending in mind even though it is a different one and not the original end which he planned when he started the manga. As you can see here:

In an interview with White-Screen.jp, Isayama has said that he's been evolving his manga, with new elements being added. However, one of the more substantial changes to the series' direction is that he has abandoned plans for an audience traumatizing ending..... With all the support that the series has received, he didn't want to slam the fans with a traumatic conclusion.

The interview is here (only in japanese) and another source of information can be found here.

In another interview he says:

It seemed like my editor wasn’t going to let the series start to be published unless I had an ending in mind.

There are high chances that the situation is like this:

He had the dark ending planned up, then he abandoned it due to the reasons above and changed the route of events to a happier end but he may or may not have a clear and set in stone happier end with all of the characters' fate decided, only a general idea which is still left to be polished.