For N1, N2, and C2 machine types, Compute Engine provides automatic sustained use discounts for all of the predefined vCPU and memory resources that you use in a region. Sustained use discounts for predefined machine types are calculated separately from custom, memory-optimized, compute-optimized, and shared-core machine types. Depending on the machine type, sustained use discounts differ between N1 and N2 machine types:
N1 machine types can receive a sustained use discount up to 30%.
N2 machine types can receive a sustained use discount up to 20%.