Appstream Cost question

As per docs, for Always-On fleet instances, "all instances that are running are charged the applicable running instance fee", however only if they are running. AWS makes best effort as stated "AppStream 2.0 monitors your fleet utilization and performs automatic adjustments to fleet capacity to meet your user demand at the lowest possible cost.".

For On-Demand fleet instances, "only when the instances are used for streaming sessions. Instances in On-Demand fleets that are not being used for streaming sessions are charged a small hourly stopped instance fee".

So, you are charged for running instances. for instances where there is no streaming sessions you are charged as well but the stopped instance fee instead of running (e.g. $0.025 instead of $0.10).

Take a look here, it gives very good overview and great example https://aws.amazon.com/appstream2/pricing/.