I will discuss the effective action of F-theory at order alpha'^3 from a twelve-dimensional perspective. First, I will show that all the known eight-derivative couplings of type IIB supergravity involving graviton and axio-dilaton naturally descend from pure gravity in twelve dimensions. Then, upon compactification on elliptic Calabi-Yau fourfolds, I will show how the non-trivial vacuum profile of the axio-dilaton leads to a new, genuinely N=1 correction to the four-dimensional effective action.
