Flipped Seat
For President, U.S. Senate, U.S. House and Governor races, the new flippedSeat field in JSON (FlippedSeat in XML) indicates whether the race winner flipped the seat by beating an incumbent from an opposing political party; for example, a Democrat flipped a Senate seat by beating an incumbent Republican.
In JSON: flippedSeat: true (flipped); flippedSeat: false (not flipped)
Party Race Call
For races where all candidates are from the same party, the new partyRaceCall field in JSON indicates that the race will be called for the party they belong to; for example, partyRaceCall: "Dem"
From the changelog: