  The surfaces of perovskite oxides affect their functional properties, and
while a bulk-truncated (1$\times$1) termination is generally assumed, its
existence and stability is controversial. Here, such a surface is created by
cleaving the prototypical SrTiO$_3$(001) in ultra-high vacuum, and its response
to thermal annealing is observed. Atomically resolved nc-AFM shows that
intrinsic point defects on the as-cleaved surface migrate at temperatures above
200\,$^\circ$C. At 400--500\,$^\circ$C, a disordered surface layer forms,
albeit still with a (1$\times$1) pattern in LEED. Purely TiO$_2$-terminated
surfaces, prepared by wet-chemical treatment, are also disordered despite their
(1$\times$1) periodicity in LEED.
