How to use Reserved Instances for Gamelift fleets

You have a few options in Gamelift including Gamelift Spot which, if suitable for you, is likely to yield the best savings. Or Gamelift Anywhere allows you to use self-managed EC2 instances which you can cover with Reservations or Savings Plans. Savings Plans are definitely a better option than Reservations for compute resources - see https://www.linkedin.com/pulse/aws-savings-plans-reservations-perils-over-optimising-steve-kinsman/ for a discussion of trade-offs.