  We report the first observation of single-top-quark production in the s
channel through the combination of the CDF and D0 measurements of the cross
section in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV.
The data correspond to total integrated luminosities of up to 9.7 fb-1 per
experiment. The measured cross section is $\sigma_s = 1.29^{+0.26}_{-0.24}$ pb.
The probability of observing a statistical fluctuation of the background to a
cross section of the observed size or larger is $1.8 \times 10^{-10}$,
corresponding to a significance of 6.3 standard deviations for the presence of
an s-channel contribution to the production of single-top quarks.
