Xbox One users who wanted to continue using their Kinect sensor with the Xbox One S had a pretty extensive grace period during which they could grab an adapter. The grace period has finally worn off this month, so people who want to use their old Xbox One Kinect for their shiny new Xbox One S are going to need to drop the full $40 on an adapter.
There wasn't much fanfare about the cancellation of the deal - in fact, it wasn't really announced anywhere. The deal was branded with a "limited time only" stamp from the get-go, with a vague "March 2017" end date. The timeline was accurate, but it would have been nice to see something of an announcement for exactly when the deal finished up. According to Polygon's estimation, the deal finished its lifespan around the middle of March.
While this shouldn't affect too many people, as the early adopters of the Xbox One S have had plenty of time to move over, it's important for other Xbox One S owners not to get their hopes up about getting themselves a free adapter. If you're interested in picking one up, you can grab it from the Microsoft store for $40.