  We use synthetic sightlines drawn through snapshots of the Technicolor Dawn
simulations to explore how the statistics of neutral oxygen OI absorbers
respond to hydrogen reionization. The ionization state of the circumgalactic
medium (CGM) initially roughly tracks that of the intergalactic medium, but
beginning at $z=8$ the CGM grows systematically more neutral owing to
self-shielding. Weak absorbers trace diffuse gas that lies farther from halos,
hence they are ionized first, whereas stronger systems are less sensitive to
reionization. The overall OI covering fraction decreases slowly with time owing
to competition between ongoing enrichment and gradual encroachment of
ionization fronts into increasingly overdense gas. While the declining covering
fraction is partially offset by continued formation of new halos, the
ionization of the diffuse gas causes the predicted line-of-sight incidence rate
of OI absorbers to decline abruptly at the overlap epoch, in qualitative
agreement with observations. In comparison to the recently-observed equivalent
width (EW) distribution at $z\approx6$, the simulations underproduce systems
with $EW \geq 0.1 \unicode{x212B}$, although they reproduce weaker systems with
$EW \geq 0.05 \unicode{x212B}$. By $z\approx5$, the incidence of $EW < 0.1
\unicode{x212B}$ systems are overproduced, consistent with previous indications
that the simulated ionizing background is too weak at $z<6$. The summed column
densities of SiII and SiIV trace the total oxygen column, and hence the ratio
of the OI and SiII + SiIV comoving mass densities traces the progress of
reionization. This probe may prove particularly useful in the regime where
$x_{HI} > 10\%$
