Stadia lets you join a friend's game without an invite
 

Google is gradually bringing more and more useful features to Stadia, many of which probably should have been available from the outset. It's still ridiculous how long it took to add a search function to the store, for one thing. Shortly after the arrival of free trials for some more titles, Google is rolling out an option to join a friend's game without an invite.

https://www.engadget.com/google-stad...7.html?src=rss