Here is a lengthy interview where he discusses this at length (with a timestamp where he says exactly that String Theory, the precise mathematical model, doesn't describe the real world):

https://www.youtube.com/watch?v=2p_Hlm6aCok&t=10m15s

This also references this podcast discussion between Leonard Susskind and Lawrence Krauss, where they discuss the same thing:

https://www.youtube.com/watch?v=qhszd_wqAgQ

Note that he still thinks that there is a way to produce some kind of similar theory, "a string theory" as opposed to "String Theory", could be the best answer.

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aurareturn 2 hours ago | parent [-]

https://www.reddit.com/r/AskPhysics/comments/1kolwxm/last_ye...

According to this Reddit thread, he doesn't say it's "dead in the water" at all. It's just a version of string theory.

This is what I'm afraid of. People who aren't qualified spreading fake news on string theory.

I don't claim to be qualified. I just want to call out HN people who are extremely confident that string theory is dead but has no background in physics.

	▲	simiones 2 hours ago \| parent [-]
		You can listen to the podcast yourself. I explained my own understanding of his position: that String Theory, the specific mathematical structure, is categorically not a good model of the real world. He does believe that it is possible to create a different theory inspired from String Theory, "a slightly expanded version of String Theory", that could be correct. But, he also says that no version of a string theory that exists today fulfills this role. Now, if by "string theory is dead in the water" someone means that "working on a generalization of string theory is a bad idea", then they are wrong, Leonard Susskind doesn't believe that. But if by "string theory is dead in the water" they mean "there is no point in studying String Theory deeper, with its general mathematical properties, maybe with a slight tweaks, as it is right now it can't describe the real world", then this is quite clearly professor Susskind's position.