Only a select number of games are supported.

In a surprise move, Amazon Luna now offers free cloud streaming for Ubisoft games you’ve purchased on PC. An Amazon Prime subscription (or Luna+ membership) is all you need to stream games from your Ubisoft library. Simply link your Amazon and Ubisoft accounts to enjoy the fun.

Update, 12/6/22: Added clarification from Amazon

This is an interesting approach to cloud gaming that’s reminiscent of NVIDIA GeForce Now. Instead of forcing customers to pay for a Luna+ subscription, Amazon Luna will allow you to pay for free if you own a supported Ubisoft game for PC. You can also purchase Ubisoft games through Amazon Luna, and such purchases will sync with your Ubisoft account.

All Ubisoft+ games available on Amazon Luna work with this free program. For a full list of compatible games, check the Ubisoft+ games library and filter the results by “Cloud Gaming (Amazon Luna).”

Interestingly, titles offered through Ubisoft+ can now be individually purchased on Luna. These purchases are linked to your Ubisoft account, side-stepping the problem that some Stadia users are experiencing right now. (Ubisoft games purchased on Stadia weren’t synced to a Ubisoft account, which is something that companies are trying to resolve as Stadia shuts down.)

Note that Amazon Luna may make you wait in a lobby during peak hours. The service is still prioritizing Luna+ subscribers, who will continue to receive a faster and more responsive streaming experience than other users.

Source: Amazon