Xbox corporate VP Marc Whitten has revealed that the Xbox One will not require the Kinect sensor in order to function. While the Xbox One will come with the Kinect packed in and is designed to perform optimally with the peripheral attached, players will be able to use their console without attaching the Kinect.
Whitten revealed this in a Q&A session with IGN earlier today. "Games use Kinect in a variety of amazing ways from adding voice to control your squad mates to adding lean and other simple controls beyond the controller to full immersive gameplay," he said. "That said, like online, the console will still function if Kinect isn’t plugged in, although you won’t be able to use any feature or experience that explicitly uses the sensor."
This answer appears to indicate another policy change for Microsoft's new console, after a report from earlier this year stated that Kinect "must be plugged in and calibrated for the console to even function."