Playing on our office Xbox One this afternoon we were prompted to get a new system update for the console mid-session. A bit odd, but apparently this new patch improves things behind the scenes according to a tweet from Microsoft's Major Nelson.
There is no information on exactly what was remedied, but given the lack of a heads up we assume it needed to be taken care of quickly. Microsoft have previously commented they want to focus on stability over the holiday period so presumably these fixes goes towards improving stability.
According to DualShockers the next big Xbox One update is planned for February (the last big one was New Xbox Experience in November), though there is no official confirmation on when the next big one hits and what to expect from it.