From 1979 to 2016, total Antarctic sea ice extent experienced a positive trend with record wintermaxima in 2012 and 2014. Record summer minima followed within the period 2017-2024, raising the possibility that the Antarctic sea ice system might be changing state. Here we use a Bayesian reconstruction of Antarctic sea ice extent which extends the record back to 1899, to show that the sequence of extreme minima in summer Antarctic sea ice extent is unlikely to have happened in the 20th century. We show that they represent a structural change in the sea ice system, manifest by increased persistence in the sea ice extent anomalies and a strongly reduced tendency to return to the mean state. Further, our analysis suggests that we may no longer rely on the past, long-term, behavior of the sea ice system to predict its future state. Extreme conditions may characterize the future state of Antarctic sea ice.