The decay $K^{+} \to \pi^{+} \nu \bar{\nu}$, with a very precisely predicted branching ratio of less than $10^{-10}$, is one of the best candidates to reveal indirect effects of new physics at the highest mass scales. The NA62 experiment at CERN SPS is designed to measure the branching ratio of the $K^{+} \to \pi^{+} \nu \bar{\nu}$ with a decay-in-flight technique, novel for this channel. The statistics of the first sample collected with the full detector, in 2016, allows to reach the Standard Model sensitivity for $K^{+} \to \pi^{+} \nu \bar{\nu}$, entering the domain of $10^{-10}$ single event sensitivity and showing the proof of principle of the experiment. The preliminary result from the 2016 data set is presented.