Apple Arcade will reportedly cost $4.99 per month after a one-month free trial. A promotional message found by 9to5Mac in one of the APIs used by the Apple Store app, and it contained this pricing info.
When it launches, Apple Arcade will support Family Sharing. That means that you and up to five family members will be able to share an Apple Arcade subscription.
Apple Arcade is a service that'll give you access to more than 100 new and exclusive games on iPhone, iPad, Mac, and Apple TV, and your progress will sync across platforms. You'll also be able to download and play any of them offline, and there will be no ads or additional purchases required.
Apple Arcade is set to launch this fall, and it's possible that we'll learn more at Apple's rumored September 10 event.