Two approaches have dominated formulations designed to capture small departures from unit root autoregressions. The …rst involves deterministic departures that include local-to-unity (LUR) and mildly (or moderately) integrated (MI) speci…cations where departures shrink to zero as the sample size n ! 1. The second approach allows for stochastic departures from unity, leading to stochastic unit root (STUR) speci…cations. This paper introduces a hybrid local stochastic unit root (LSTUR) speci…cation that has both LUR and STUR components and allows for endogeneity in the time varying coe¢ cient that introduces structural elements to the autoregression. This hybrid model generates trajectories that, upon normalization, have non-linear di¤usion limit processes that link closely to models that have been studied in mathematical …nance, particularly with respect to option pricing. It is shown that some LSTUR parameterizations have a mean and variance which are the same as a random walk process but with a kurtosis exceeding 3, a feature which is consistent with much …nancial data. We develop limit theory and asymptotic expansions for the process and document how inference in LUR and STUR autoregressions is a¤ected asymptotically by ignoring one or the other component in the more general hybrid generating mechanism. In particular, we show how con…dence belts constructed from the LUR model are a¤ected by the presence of a STUR component in the generating mechanism. The import of these …ndings for empirical research are explored in an application to the spreads on US investment grade corporate debt.