Leapsecond 2016 complete.
You can see that Google starts its 20 hour leap-second “skew” 10 hours before the event and then skews back to the real time. Everyone else stays correct and then has a short error as they “leap” the second and then come back into correct time.
A close look shows that a few minutes passed before all the non-google NTP servers were back in sync with TimeKeeper’s GPS source as TimeKeeper slewed over short time. The default TimeKeeper slew behavior is designed to retain data integrity with unique event timestamps while not imposing a long period of inaccurate time.