Anatase titanium dioxide (TiO2) is one of the most widely used metal oxides for applications ranging from photo-catalysis and self-cleaning windows to biomedical devices. Oxygen vacancies in this material have been shown to give rise to localized defect states within the band-gap (in-gap (IG)) as well as highly delocalized (conductive) two-dimensional electron gas (2DEG) states in proximity of the surface. We present results for the oxygen vacancy induced IG and 2DEG states on the reconstructed anatase TiO2 (001) - (1x4) surface showing that these originate from sites localized directly at the surface and in the subsurface respectively. At variance with what was found for anatase (101), the energy barrier for subsurface --> surface migration of oxygen vacancies is quite high at the anatase (001) surface, making them much less reactive when exposed to gaseous O2. For the same reason, 2DEG states are also much more robust than IG states when exposed to O2.