  A measurement of the $t\bar{t}Z$ and $t\bar{t}W$ production cross sections in
final states with either two same-charge muons, or three or four leptons
(electrons or muons) is presented. The analysis uses a data sample of
proton-proton collisions at $\sqrt{s} = 13$ TeV recorded with the ATLAS
detector at the Large Hadron Collider in 2015, corresponding to a total
integrated luminosity of 3.2 fb$^{-1}$. The inclusive cross sections are
extracted using likelihood fits to signal and control regions, resulting in
$\sigma_{t\bar{t}Z} = 0.9 \pm 0.3$ pb and $\sigma_{t\bar{t}W} = 1.5 \pm 0.8$
pb, in agreement with the Standard Model predictions.
