Google is currently offering a free Google Stadia Kit for those that have had an active YouTube Premium subscription before November 6th. Unfortunately, this means that those who signed up for a subscription after this date will not be eligible. If you have had an active subscription, you can head to the Google Stadia Official Website to attempt to claim your free kit.
The kit is the original Google Stadia kit that includes the Google Stadia Controller and a Chromecast Ultra. Do note that this is not the new Chromecast that was recently released by Google. The kit does not come with a Google Stadia Pro subscription, which will run you an additional $9.99 a month.
Even if you are not a Google Stadia user, getting a $100 kit for free is rather lovely, and with Google recently dabbling in free game demo's, it may not be a bad idea to get your hands on one to try out Stadia.