Integrable models in string theory?

[pivoxa15]

In the official string site, why didn't they recommend studying integrable models in the mathematics section?

String theory itself is an integrable model, no?

 

[Demystifier]

Free string theory, just as any free theory, is integrable. Interacting string theory, like most interacting theories, is not integrable. The curious thing about string theory is that the interacting theory is governed by the same FREE Lagrangian appearing in the free theory as well.