arXiv:2611.14259v1 Announce Type: new Abstract: This paper investigates probabilistic reachability for discrete-time linear stochastic systems subject to bounded multiplicative uncertainty and potentially unbounded additive noise. To address the conservatism of reachable sets constructed solely from covariance information, we develop two complementary approaches based on sub-Gaussian and sub-exponential matrix moment-generating-function characterizations. The sub-Gaussian approach relies on a worst-case envelope over the uncertainty support, whereas the sub-exponential approach exploits expectation-based propagation of the matrix variance proxy. Both approaches are used to construct probabilistic reachable sets with explicit probability guarantees, considering ellipsoidal confidence regions and half-space bounds. For the latter, we derive a necessary and sufficient condition under which the sub-exponential chance-constraint margin is no larger than its sub-Gaussian counterpart. Numerical results show that the proposed bounds can be less conservative than those based on the covariance, and illustrate the complementary nature of the two approaches across probability levels.