We show that in generic one-dimensional Hamiltonian lattices the diffusion coefficient of the maximum Lyapunov exponent diverges in the thermodynamic limit. We trace this back to the long-range correlations associated with the evolution of the hydrodynamic modes. In the case of normal heat transport, the divergence is even stronger, leading to the breakdown of the usual single-function Family-Vicsek scaling ansatz. A similar scenario is expected to arise in the evolution of rough interfaces in the presence of suitably correlated background noise. DOI: 10.1103/PhysRevLett.117.034101 Lyapunov exponents (LEs) are dynamical invariants that provide a detailed characterization of low-dimensional as well as spatiotemporal chaos [1]: they indeed allow estimating the fractal dimension, the Kolmogorov-Sinai entropy, and allow us to ascertain the extensivity of the underlying dynamical regime. LEs are average quantities, defined as the infinite-time limit of the so-called finite-time Lyapunov exponents (FTLEs). Interestingly, also the temporal fluctuations of FTLEs carry important information that is ultimately encoded in yet another invariant: a suitable large deviation function. Fluctuations help to shed light on important phenomena such as intermittency, strange nonchaotic attractors, and stable chaos [1].In dissipative systems with many degrees of freedom, the fluctuations of the largest FTLE have been investigated in various numerical setups such as a shell model for the energy cascade in turbulence [2], a cellular automaton [3], molecular dynamics simulations [4], coupled-map lattice models [5,6], and a variety of continuous-time models [7,8]. In particular, in spatially extended systems like those in Refs. [5,6,8], the dynamics of Lyapunov vectors, i.e., perturbation fields, is formally equivalent to the evolution of rough interfaces in a noisy environment, the LE corresponding to the velocity of the interface [9,10]. This relationship is essentially based on the interpretation of the logarithm of the local amplitude of the perturbation with the height hðx; tÞ of a suitable interface. As a result, the same "physics" can be found in two significantly different contexts. In particular, the universality class of roughening phenomena identified by the Kardar-ParisiZhang (KPZ) equation [11] includes also the perturbation evolution in spatially extended chaotic systems [9,10,12].In spite of its broadness, the KPZ universality class does not encompass Hamiltonian models [13,14]. Preliminary studies revealed different critical properties and generically attributed the anomalous scaling to long-range correlations [13]. Later on, powerful methods for the characterization of large deviations revealed that extreme fluctuations of the FTLE in the classical Fermi-Pasta-Ulam (FPU-β) chain [15] correspond to atypical solutions of solitonlike and chaotic-breather dynamics [6,16]. However, it is not clear to what extent they are responsible for the anomalous non-KPZ behavior.In this Letter we study the diffusion coefficient D of t...