"This means you can jumpstart the iHeartRadio experience from right inside your music library to listen to thousands of endlessly, diverse live radio stations from across the U.S. – including pop, country, urban, rock, talk, college and more – or create a custom station based on a song you are listening to, right from the Groove app."
The new feature does require users have the iHeartRadio app already installed, but it does not require a subscription to the Groove Music Pass. Microsoft says:
"To enjoy iHeartRadio without a Groove Music Pass, simply go to the artist's page that best fits your mood. If there's an artist-based custom radio station available from iHeartRadio, you will see the option right on the page. Click on it whenever you're ready to listen – we will even help you install the iHeartRadio app if you don't currently have it – and then just lean back and enjoy your station."