I don't think Susskind works on string theory proper at all anymore. He works on the AdS/CFT stuff, which is compatible with and motivated by stringy approache

I don't think Susskind works on string theory proper at all anymore. He works on the AdS/CFT stuff, which is compatible with and motivated by stringy approaches, but is logically quite independent. Related: https://www.math.columbia.edu/~woit/wordpress/?p=6252 https://www.math.columbia.edu/~woit/wordpress/?p=6252