YouTube offers 3 months of Premium membership for free
The offer is only available in the US and is limited to new users, which means that if you subscribed to YouTube Red or Google Play Music in the past, you won't qualify. Obviously, you can cancel your subscription a week before the trial expires if you don't want to start paying for YouTube Premium.
Currently, one month of YouTube Premium costs $11.99, which will give you access to videos, as well as YouTube Music, Google's music streaming service that recently replaced Play Music. To subscribe and receive 3 months of service for free, simply visit the YouTube Premium website until December 6.